1,100,000 Shares NorthWestern Corporation Common Stock, $0.01 Par Value UNDERWRITING AGREEMENT

As Representative of the Several Underwriters

Dear Sirs:

1.Introductory. NorthWestern Corporation, a Delaware corporation (“Company”), agrees with the several Underwriters named in Schedule A hereto (“Underwriters”), for whom you are acting as Representative (the “Representative”), to issue and sell to the several Underwriters 1,100,000 shares (“Offered Securities”) of its common stock, $0.01 par value per share.

2.Representations and Warranties of the Company. The Company represents and warrants to, and agrees with, the several Underwriters that:

(a)The Company has filed with the Commission a registration statement on Form S-3 (No. 333-202126), including a related prospectus, covering the registration of the Offered Securities under the Act, which has become effective. “Registration Statement” at any particular time means such registration statement in the form then filed with the Commission, including any amendment thereto, any document incorporated by reference therein and all 430B Information and all 430C Information with respect to such registration statement, that in any case has not been superseded or modified. “Registration Statement” without reference to a time means the Registration Statement as of the Effective Time. For purposes of this definition, 430B Information shall be considered to be included in the Registration Statement as of the time specified in Rule 430B.

For purposes of this Agreement:

“430B Information” means information included in a prospectus then deemed to be a part of the Registration Statement pursuant to Rule 430B(e) or retroactively deemed to be a part of such Registration Statement pursuant to Rule 430B(f).

“430C Information” means information included in a prospectus then deemed to be a part of the Registration Statement pursuant to Rule 430C.

“Act” means the Securities Act of 1933, as amended.

“Applicable Time” means 5:30 P.M. (Eastern time) on the date of this Agreement.

“Closing Date” has the meaning defined in Section 3 hereof.

“Commission” means the Securities and Exchange Commission.

“Effective Time” of the Registration Statement relating to the Offered Securities means the time of the first contract of sale for the Offered Securities.

“Exchange Act” means the Securities Exchange Act of 1934, as amended.

“Final Prospectus” means the Statutory Prospectus relating to the Offered Securities that was first filed pursuant to Rule 424(b) after the Applicable Time.

“General Use Issuer Free Writing Prospectus” means any Issuer Free Writing Prospectus that is intended for general distribution to prospective investors, as evidenced by its being so specified in Schedule B-2 hereto.

“Issuer Free Writing Prospectus” means any “issuer free writing prospectus,” as defined in Rule 433, relating to the Offered Securities in the form filed or required to be filed with the Commission or, if not required to be filed, in the form retained in the Company’s records pursuant to Rule 433(g).

“Limited Use Issuer Free Writing Prospectus” means any Issuer Free Writing Prospectus that is not a General Use Issuer Free Writing Prospectus.

“Rules and Regulations” means the rules and regulations of the Commission.

“Securities Laws” means, collectively, the Sarbanes-Oxley Act of 2002 (“Sarbanes-Oxley”), the Act, the Exchange Act, the Rules and Regulations, the auditing principles, rules, standards and practices applicable to auditors of “issuers” (as defined in Sarbanes-Oxley) promulgated or approved by the Public Company Accounting Oversight Board and, as applicable, the rules of the New York Stock Exchange and the NASDAQ Stock Market (“Exchange Rules”).

“Statutory Prospectus” with reference to a particular time means the prospectus that is included in the Registration Statement immediately prior to that time, including all 430B Information and all 430C Information with respect to the Registration Statement. For purposes of the foregoing definition, 430B Information shall be considered to be included in the Statutory Prospectus as of the actual time that form of prospectus (including a prospectus supplement) is filed with the Commission pursuant to Rule 424(b) and not retroactively.

Unless otherwise specified, a reference to a “rule” is to the indicated rule under the Act.

(b)(i) (A) At the time the Registration Statement initially became effective, (B) at the time of each amendment thereto for the purposes of complying with Section

10(a)(3) of the Act (whether by post-effective amendment, incorporated report or form of prospectus), (C) at the Effective Time relating to the Offered Securities and (D) on the Closing Date, the Registration Statement conformed and will conform in all material respects to the requirements of the Act and the Rules and Regulations and did not and will not include any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary to make the statements therein not misleading and (ii) (A) on its date, (B) at the time of filing the Final Prospectus pursuant to Rule 424(b) and (C) on the Closing Date, the Final Prospectus will conform in all material respects to the requirements of the Act and the Rules and Regulations, and will not include any untrue statement of a material fact or omit to state any material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading. The preceding sentence does not apply to statements in or omissions from any such document based upon written information furnished to the Company by any Underwriter through the Representative specifically for use therein, it being understood and agreed that the only such information is that described as such in Section 8(b) hereof.

(c)(i) (A) At the time of initial filing of the Registration Statement, (B) at the time of the most recent amendment thereto for the purposes of complying with Section 10(a)(3) of the Act (whether such amendment was by post-effective amendment, incorporated report filed pursuant to Section 13 or 15(d) of the Exchange Act or form of prospectus), and (C) at the time the Company or any person acting on its behalf (within the meaning, for this clause only, of Rule 163(c)) made any offer relating to the Offered Securities in reliance on the exemption of Rule 163, the Company was a “well known seasoned issuer” as defined in Rule 405, including not having been an “ineligible issuer” as defined in Rule 405.

(ii)    The Registration Statement is an “automatic shelf registration statement,” as defined in Rule 405, that initially became effective within three years of the date of this Agreement.

(iii)    The Company has not received from the Commission any notice pursuant to Rule 401(g)(2) objecting to use of the automatic shelf registration statement form. If at any time when Offered Securities remain unsold by the Underwriters the Company receives from the Commission a notice pursuant to Rule 401(g)(2) or otherwise ceases to be eligible to use the automatic shelf registration statement form, the Company will (i) promptly notify the Representative, (ii) promptly file a new registration statement or post-effective amendment on the proper form relating to the Offered Securities, in a form satisfactory to the Representative, (iii) use its reasonable best efforts to cause such registration statement or post-effective amendment to be declared effective as soon as practicable, and (iv) promptly notify the Representative of such effectiveness. The Company will take all other action necessary or appropriate to permit the public offering and sale of the Offered Securities to continue as contemplated in the registration statement that was the subject of the Rule 401(g)(2) notice or for which the Company has otherwise become ineligible.

References herein to the Registration Statement shall include such new registration statement or post-effective amendment, as the case may be.

(iv)    The Company has paid or shall pay the required Commission filing fees relating to the Offered Securities within the time required by Rule 456(b)(1) without regard to the proviso therein and otherwise in accordance with Rules 456(b) and 457(r).

(d)As of the Applicable Time, neither (i) the General Use Issuer Free Writing Prospectus(es), if any, issued at or prior to the Applicable Time and the preliminary prospectus supplement, dated September 29, 2015, including the base prospectus, dated February 17, 2015 (which is the most recent Statutory Prospectus distributed to investors generally), and the other information stated in Schedule B-1 to this Agreement to be included in the General Disclosure Package, all considered together (collectively, the “General Disclosure Package”), nor (ii) any individual Limited Use Issuer Free Writing Prospectus, when considered together with the General Disclosure Package, included any untrue statement of a material fact or omitted to state any material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading. The preceding sentence does not apply to statements in or omissions from any Statutory Prospectus or any Issuer Free Writing Prospectus in reliance upon and in conformity with written information furnished to the Company by any Underwriter through the Representative specifically for use therein, it being understood and agreed that the only such information furnished by any Underwriter consists of the information described as such in Section 8(b) hereof.

(e)Each Issuer Free Writing Prospectus, as of its issue date and at all subsequent times through the completion of the public offer and sale of the Offered Securities or until any earlier date that the Company notified or notifies the Representative as described in the next sentence, did not, does not and will not include any information that conflicted, conflicts or will conflict with the information then contained in the Registration Statement. If at any time following issuance of an Issuer Free Writing Prospectus there occurred or occurs an event or development as a result of which such Issuer Free Writing Prospectus conflicted or would conflict with the information then contained in the Registration Statement or as a result of which such Issuer Free Writing Prospectus, if republished immediately following such event or development, would include an untrue statement of a material fact or omitted or would omit to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading, (i) the Company has promptly notified or will promptly notify the Representative and (ii) the Company has promptly amended or will promptly amend or supplement such Issuer Free Writing Prospectus to eliminate or correct such conflict, untrue statement or omission.

(f)As of the date of this Agreement, the Company has an authorized and outstanding capitalization as set forth in the consolidated balance sheet as of June 30, 2015, and there has been no material change in such information since that date (subject to the issuance of securities under the Company’s (i) dividend reinvestment and direct stock purchase plan, (ii) employee stock purchase plan, (iii) director and executive

compensation plans, including deferred compensation plans and (iv) other employee benefit plans and the grant of options or other equity awards under any such director and executive compensation plans); as of the date of this Agreement, all of the issued and outstanding shares of capital stock of the Company have been duly authorized and validly issued and are fully paid and non-assessable, have been issued in compliance with all applicable securities laws and were not issued in violation of any preemptive right, resale right, right of first refusal or similar right; prior to the Closing Date, the Offered Securities will be duly listed, and admitted and authorized for trading, subject to official notice of issuance, on the New York Stock Exchange (the “NYSE”).

(g)The Company has been duly incorporated and is validly existing as a corporation in good standing under the laws of the State of Delaware, with full corporate power and authority to own, lease and operate its properties and conduct its business as described in the General Disclosure Package and the Final Prospectus, to execute and deliver this Agreement and to issue, sell and deliver the Offered Securities as contemplated herein.

(h)The Company is duly qualified to do business as a foreign corporation and is in good standing in each jurisdiction where the ownership or leasing of its properties or the conduct of its business requires such qualification, except where the failure to be so qualified and in good standing would not, individually or in the aggregate, (i) have a material adverse effect on the business, properties, financial condition, results of operations or prospects of the Company and the Subsidiaries (as defined below) taken as a whole, (ii) prevent or materially interfere with consummation of the transactions contemplated hereby or (iii) result in the delisting of the Company’s common stock from the NYSE (the occurrence of any such effect or any such prevention or interference or any such result described in the foregoing clauses (i), (ii) and (iii) being herein referred to as a “Material Adverse Effect”).

(i)As of the date hereof, the Company has no subsidiaries (as defined under the Act) other than those subsidiaries listed on Schedule C hereto (collectively, the “Subsidiaries”), and the Company has no “significant subsidiary,” as that term is defined in Rule 1-02(w) of Regulation S-X under the Act; complete and correct copies of the charters and the bylaws of the Company and each Subsidiary and all amendments thereto have been delivered to the Representative; each Subsidiary has been duly incorporated and is validly existing as a corporation in good standing under the laws of the jurisdiction of its incorporation, with full corporate power and authority to own, lease and operate its properties and to conduct its business as described in the General Disclosure Package and the Final Prospectus; each Subsidiary is duly qualified to do business as a foreign corporation and is in good standing in each jurisdiction where the ownership or leasing of its properties or the conduct of its business requires such qualification, except where the failure to be so qualified and in good standing would not, individually or in the aggregate, have a Material Adverse Effect; all of the outstanding shares of capital stock of each of the Subsidiaries have been duly authorized and validly issued, are fully paid and non-assessable, have been issued in compliance with all applicable securities laws, were not issued in violation of any preemptive right, resale right, right of first refusal or similar right and are owned by the Company subject to no security interest, other encumbrance

or adverse claims; no options, warrants or other rights to purchase, agreements or other obligations to issue or other rights to convert any obligation into shares of capital stock or ownership interests in the Subsidiaries are outstanding.

(j)The Offered Securities have been duly and validly authorized and, when issued and delivered against payment therefor as provided herein, will be duly and validly issued, fully paid and non-assessable and free of statutory and contractual preemptive rights, resale rights, rights of first refusal and similar rights; the Offered Securities, when issued and delivered against payment therefor as provided herein, will be free of any restriction upon the voting or transfer thereof pursuant to the Company’s charter or bylaws or any agreement or other instrument to which the Company is a party.

(k)The capital stock of the Company, including the Offered Securities, conforms in all material respects to each description thereof, if any, contained or incorporated by reference in the General Disclosure Package and the Final Prospectus.

(l)The Company has full corporate power and authority to enter into this Agreement. This Agreement has been duly authorized, executed and delivered by the Company.

(m)Except as disclosed in the General Disclosure Package and the Final Prospectus, neither the Company nor any of the Subsidiaries is (i) in violation of its respective charters or by-laws or other governance documents or (ii) in default in the performance of any obligation, agreement, covenant or condition contained in any indenture, loan agreement, mortgage, lease or other agreement or instrument to which the Company or any of the Subsidiaries is a party or by which the Company or any of the Subsidiaries or their respective property is bound, or (iii) in violation of any federal, state, local or foreign law, regulation or rule, or any rule or regulation of any self-regulatory organization or other non-governmental regulatory authority (including, without limitation, the rules and regulations of the NYSE), or any decree, judgment or order applicable to it or any of its properties, except for such violations or defaults (excluding clause (i)) as would not have, or reasonably be expected to have, a Material Adverse Effect.

(n)The execution, delivery and performance of this Agreement, the issuance and sale of the Offered Securities and the consummation of the transactions contemplated hereby will not result in a breach or violation of any of the terms and provisions of, or constitute a default under, (i) any statute, any rule, regulation or order of any governmental agency or body or any court, domestic or foreign, having jurisdiction over the Company or any Subsidiary of the Company or any of their properties, or (ii) any agreement or instrument to which the Company or any such Subsidiary is a party or by which the Company or any such Subsidiary is bound or to which any of the properties of the Company or any such Subsidiary is subject, or (iii) the charter or by-laws of the Company or any such Subsidiary, except, in the case of (i) and (ii) above, for breaches or violations that would not, individually or in the aggregate, have a Material Adverse Effect, and the Company has full power and authority to authorize, issue and sell the Offered Securities as contemplated by this Agreement.

(o)No approval, authorization, consent or order of or filing with any federal, state, local or foreign governmental or regulatory commission, board, body, authority or agency, or of or with any self-regulatory organization or other non-governmental regulatory authority (including, without limitation, the NYSE), or approval of the stockholders of the Company, is required in connection with the issuance and sale of the Offered Securities or the consummation by the Company of the transactions contemplated hereby, other than (i) the NYSE’s approval of the Company’s supplemental listing application for the Offered Securities, (ii) registration of the Offered Securities under the Act, which has been effected, (iii) order of the Montana Public Service Commission (the “MPSC”), (iv) order of the Federal Energy Regulatory Commission (the “FERC”), (v) any necessary qualification under the securities or blue sky laws of the various jurisdictions in which the Offered Securities are being offered by the several Underwriters or (vi) qualification of the offering of the Offered Securities under the Conduct Rules of the Financial Industry Regulatory Authority, Inc. (“FINRA”).

(p)The FERC has issued an appropriate order or orders with respect to the issuance and sale of the Offered Securities in accordance with this Agreement (the “FERC Order”); and the FERC Order is in full force and effect and the issuance and sale of the Offered Securities pursuant to this Agreement is in conformity with the terms of the FERC Order.

(q)The MPSC has issued an appropriate order or orders with respect to the issuance and sale of the Offered Securities in accordance with this Agreement (the “MPSC Order”); and the MPSC Order is in full force and effect and the issuance and sale of the Offered Securities pursuant to this Agreement is in conformity with the terms of the MPSC Order.

(r)Except as described in the General Disclosure Package and the Final Prospectus, (i) no person has the right, contractual or otherwise, to cause the Company to issue or sell to it any securities or shares of any other capital stock or other equity interests of the Company, (ii) no person has any preemptive rights, resale rights, rights of first refusal or other rights to purchase any securities or shares of any other capital stock of or other equity interests in the Company and (iii) no person has the right to act as an underwriter, agent, financial advisor to the Company or in any similar capacity in connection with the offer and sale of the Offered Securities; no person has the right, contractual or otherwise, to cause the Company to register under the Act any securities or shares of any other capital stock of or other equity interests in the Company, or to include any such shares or interests in the Registration Statement or the offering contemplated thereby.

(s)The Company and the Subsidiaries possess adequate certificates, licenses, approvals, franchises, authorizations or permits (collectively, “Governmental Licenses”) issued by the appropriate federal, state, local or foreign regulatory agencies or bodies necessary to conduct the business now operated by them, except where the failure to have such Governmental Licenses would not, individually or in the aggregate, have a Material Adverse Effect; and have not received any notice of proceedings relating to the revocation or modification of any such Governmental Licenses that, if determined

adversely to the Company or any of the Subsidiaries, would individually or in the aggregate result in a Material Adverse Effect.

(t)Except as disclosed in the General Disclosure Package and the Final Prospectus, to the Company’s knowledge, there are no actions, suits, claims, investigations or proceedings pending or threatened or contemplated to which the Company or any of the Subsidiaries or any of their respective directors or officers is or would be a party or of which any of their respective properties is or would be subject at law or in equity, before or by any federal, state, local or foreign governmental or regulatory commission, board, body, authority or agency, or before or by any self-regulatory organization or other non-governmental regulatory authority (including, without limitation, the NYSE), except any such action, suit, claim, investigation or proceeding which, if resolved adversely to the Company or any Subsidiary, would not, individually or in the aggregate, have a Material Adverse Effect.

(u)Deloitte & Touche LLP, who audited the annual consolidated financial statements of the Company and the Subsidiaries incorporated by reference in the General Disclosure Package and the Final Prospectus, is an independent registered public accounting firm with respect to the Company within the meaning of the Act and the rules and regulations thereunder.

(v)The financial statements included or incorporated by reference in the General Disclosure Package and the Final Prospectus, together with the related notes and schedules, and the interactive data in eXtensible Business Reporting Language included as an exhibit to the Registration Statement, present fairly the consolidated financial position of the Company and the Subsidiaries as of the dates indicated and the consolidated results of operations, cash flows and changes in stockholders’ equity of the Company and the Subsidiaries for the periods specified and have been prepared in compliance with the applicable requirements of the Act and Exchange Act and in conformity with U.S. generally accepted accounting principles applied on a consistent basis during the periods involved; the other financial and statistical data contained or incorporated by reference in the General Disclosure Package and the Final Prospectus are accurately and fairly presented in all material respects and prepared on a basis consistent with the financial statements and books and records of the Company and the Subsidiaries; there are no financial statements (historical or pro forma) that are required to be included or incorporated by reference in the Registration Statement, the General Disclosure Package or the Final Prospectus that are not included or incorporated by reference as required; and all disclosures contained or incorporated by reference in the Registration Statement, the General Disclosure Package or the Final Prospectus regarding “non-GAAP financial measures” (as such term is defined in Regulation G under the Exchange Act) comply with Regulation G under the Exchange Act and Item 10 of Regulation S-K under the Act, to the extent applicable.

(w)Since the date of the latest audited financial statements incorporated by reference in the General Disclosure Package and the Final Prospectus, except as disclosed in the General Disclosure Package and the Final Prospectus, there has been no material adverse change, nor any development or event involving a prospective material adverse

change, in the condition (financial or other), business, properties or results of operations of the Company and the Subsidiaries taken as a whole.

(x)Neither the Company nor any Subsidiary is, and, after giving effect to the offering and sale of the Offered Securities, none of them will be, an “investment company” or an entity “controlled” by an “investment company,” as such terms are defined in the Investment Company Act of 1940, as amended.

(y)Except as disclosed in the General Disclosure Package and the Final Prospectus, the Company and the Subsidiaries and their respective properties, assets and operations are in compliance with, and the Company and each of the Subsidiaries hold all permits, authorizations and approvals required under, Environmental Laws (as defined below), except to the extent that failure to so comply or to hold such permits, authorizations or approvals would not, individually or in the aggregate, have a Material Adverse Effect; except as disclosed in the General Disclosure Package and the Final Prospectus, and except as would not, individually or in the aggregate, have a Material Adverse Effect, neither the Company nor any of the Subsidiaries (i) is the subject of any investigation, (ii) has received any notice or claim, (iii) is a party to or affected by any pending or, to the Company’s knowledge, threatened action, suit or proceeding, (iv) is bound by any judgment, decree or order or (v) has entered into any agreement, in each case relating to any alleged violation of any Environmental Law or any actual or alleged release or threatened release or cleanup at any location of any Hazardous Materials (as defined below) (as used herein, “Environmental Law” means any federal, state, local or foreign law, statute, ordinance, rule, regulation, order, decree, judgment, injunction, permit, license, authorization or other binding requirement, or common law, relating to health, safety or the protection, cleanup or restoration of the environment or natural resources, including those relating to the distribution, processing, generation, treatment, storage, disposal, transportation, other handling or release or threatened release of Hazardous Materials, and “Hazardous Materials” means any material (including, without limitation, pollutants, contaminants, hazardous or toxic substances or wastes) that is regulated by or may give rise to liability under any Environmental Law).

(z)The shares of common stock of the Company are an “actively-traded security” under Rule 101 of Regulation M under the Exchange Act.

(aa)The Company and each of the Subsidiaries maintain a system of internal accounting controls sufficient to provide reasonable assurance that (i) transactions are executed in accordance with management’s general or specific authorization; (ii) transactions are recorded as necessary to permit preparation of financial statements in conformity with generally accepted accounting principles and to maintain accountability for assets; (iii) access to assets is permitted only in accordance with management’s general or specific authorization; and (iv) the recorded accountability for assets is compared with existing assets at reasonable intervals and appropriate action is taken with respect to any differences.

(bb)    The Company has established and maintains “disclosure controls and procedures” (as such term is defined in Rule 13a-15 and 15d-15 under the Exchange Act)

and “internal control over financial reporting” (as such term is defined in Rule 13a-15 and 15d-15 under the Exchange Act); such disclosure controls and procedures are designed to ensure that material information relating to the Company and the Subsidiaries, is made known to the Company’s Chief Executive Officer and its Chief Financial Officer by others within those entities, such disclosure controls and procedures are effective to perform the functions for which they were established; and, since the end of the Company’s most recent audited fiscal year, there has been (1) no material weakness in the Company’s internal control over financial reporting (whether or not remediated) and (2) no change in the Company’s internal control over financial reporting that has materially affected, or is reasonably likely to materially affect, the Company’s internal control over financial reporting.

(cc)    All statistical or market-related data included or incorporated by reference in the General Disclosure Package and the Final Prospectus are based on or derived from sources that the Company believes to be reliable and accurate.

(dd)    The Company has not received any notice from the NYSE regarding the delisting of the shares of common stock of the Company from the NYSE.

(ee)    Except pursuant to this Agreement, neither the Company nor any of the Subsidiaries has incurred any liability for any finder’s or broker’s fee or agent’s commission in connection with the execution and delivery of this Agreement or the consummation of the transactions contemplated hereby.

(ff)    Neither the Company nor any of the Subsidiaries nor any of their respective directors, officers, nor to the Company’s knowledge, their affiliates or controlling persons, has taken, directly or indirectly, any action designed or which has constituted or might reasonably be expected to cause or result in the stabilization or manipulation of the price of any security of the Company to facilitate the sale or resale of the Offered Securities.

(gg)    To the Company’s knowledge, there are no affiliations or associations between (i) any member of the FINRA and (ii) the Company or any of the Company’s officers, directors or 5% or greater security holders or any beneficial owner of the Company’s unregistered equity securities that were acquired at any time on or after the 180th day immediately preceding the date the Registration Statement was initially filed with the Commission, except as disclosed in the Registration Statement (excluding the exhibits thereto), the General Disclosure Package and the Final Prospectus.

(hh)    The interactive data in eXtensible Business Reporting Language incorporated by reference in the Registration Statement fairly presents the information called for in all material respects and has been prepared in accordance with the Commission’s rules and guidelines applicable thereto.

(ii)    No labor dispute with the employees of the Company or any of its subsidiaries exists or, to the knowledge of the Company, is imminent that could have a Material Adverse Effect.

(jj)    None of the Company, any of the Subsidiaries or, to the knowledge of the Company, any director, officer, agent, employee, affiliate or other person acting on behalf of the Company or any of the Subsidiaries is aware of or has taken any action, directly or indirectly, that would result in a violation by such persons of the Foreign Corrupt Practices Act of 1977, as amended, and the rules and regulations thereunder (the “FCPA”), including, without limitation, making use of the mails or any means or instrumentality of interstate commerce corruptly in furtherance of an offer, payment, promise to pay or authorization of the payment of any money, or other property, gift, promise to give, or authorization of the giving of anything of value to any “foreign official” (as such term is defined in the FCPA) or any foreign political party or official thereof or any candidate for foreign political office, in contravention of the FCPA and the Company has conducted its business in compliance with the FCPA .

(kk)    The operations of the Company and the Subsidiaries are and have been conducted at all times in compliance with applicable financial recordkeeping and reporting requirements of the Currency and Foreign Transactions Reporting Act of 1970, as amended, the money laundering statutes of all jurisdictions, the rules and regulations thereunder and any related or similar rules, regulations or guidelines, issued, administered or enforced by any Governmental Entity (collectively, the “Money Laundering Laws”); and no action, suit or proceeding by or before any Governmental Entity involving the Company or any of the Subsidiaries with respect to the Money Laundering Laws is pending or, to the best knowledge of the Company, threatened.

(ll)    None of the Company, any of the Subsidiaries or, to the knowledge of the Company, any director, officer, agent, employee, affiliate or representative of the Company or any of the Subsidiaries is an individual or entity (“Person”) currently the subject or target of any sanctions administered or enforced by the United States Government, including, without limitation, the U.S. Department of the Treasury’s Office of Foreign Assets Control (“OFAC”), the United Nations Security Council (“UNSC”), the European Union, Her Majesty’s Treasury (“HMT”), or other relevant sanctions authority (collectively, “Sanctions”), nor is the Company located, organized or resident in a country or territory that is the subject of Sanctions; and the Company will not directly or indirectly use the proceeds of the sale of the Offered Securities, or lend, contribute or otherwise make available such proceeds to any Subsidiaries, joint venture partners or other Person, to fund any activities of or business with any Person, or in any country or territory, that, at the time of such funding, is the subject of Sanctions or in any other manner that will result in a violation by any Person (including any Person participating in the transaction, whether as underwriter, advisor, investor or otherwise) of Sanctions.

3.Purchase, Sale and Delivery of Offered Securities. On the basis of the representations, warranties and agreements and subject to the terms and conditions set forth herein, the Company agrees to sell to the several Underwriters, and each of the Underwriters agrees, severally and not jointly, to purchase from the Company, at a purchase price of $51.81 per share, the respective number of Offered Securities set forth opposite the names of the Underwriters in Schedule A hereto.

The Company will deliver the Offered Securities to or as instructed by the Representative for the accounts of the several Underwriters in a form reasonably acceptable to the Representative against payment of the purchase price by the Underwriters in Federal (same day) funds by wire transfer to an account at a bank acceptable to the Representative drawn to the order of the Company at the office of Hunton & Williams LLP, 200 Park Avenue, New York, New York 10166, at 9:30 A.M., New York time, on October 5, 2015, or at such other time not later than seven full business days thereafter as the Representative and the Company determine, such time being herein referred to as the “Closing Date”. For purposes of Rule 15c6-1 under the Exchange Act, the Closing Date (if later than the otherwise applicable settlement date) shall be the settlement date for payment of funds and delivery of securities for all the Offered Securities sold pursuant to the offering.

4.Offering by Underwriters. It is understood that the several Underwriters propose to offer the Offered Securities for sale to the public as set forth in the Final Prospectus.

5.Certain Agreements of the Company. The Company agrees with the several Underwriters that:

(a)Filing of Prospectuses. The Company has filed or will file each Statutory Prospectus (including the Final Prospectus) pursuant to and in accordance with Rule 424(b)(2) (or, if applicable and consented to by the Representative, subparagraph (5)) not later than the second business day following the earlier of the date it is first used or the execution and delivery of this Agreement. The Company has complied and will comply with Rule 433.

(b)Filing of Amendments; Response to Commission Requests. The Company will promptly advise the Representative of any proposal to amend or supplement the Registration Statement or any Statutory Prospectus at any time and will offer the Representative a reasonable opportunity to comment on any such amendment or supplement; and the Company will also advise the Representative promptly of (i) the filing of any such amendment or supplement, (ii) any request by the Commission or its staff for any amendment to the Registration Statement, for any supplement to any Statutory Prospectus or for any additional information, (iii) the institution by the Commission of any stop order proceedings in respect of the Registration Statement or the threatening of any proceeding for that purpose, and (iv) the receipt by the Company of any notification with respect to the suspension of the qualification of the Offered Securities in any jurisdiction or the institution or threatening of any proceedings for such purpose. The Company will use its reasonable best efforts to prevent the issuance of any such stop order or the suspension of any such qualification and, if issued, to obtain as soon as possible the withdrawal thereof.

(c)Continued Compliance with Securities Laws. If, at any time when a prospectus relating to the Offered Securities is (or but for the exemption in Rule 172 would be) required to be delivered under the Act by any Underwriter or dealer, any event occurs as a result of which the Final Prospectus as then amended or supplemented would include an untrue statement of a material fact or omit to state any material fact necessary to make the statements therein, in the light of the circumstances under which they were

made, not misleading, or if it is necessary at any time to amend the Registration Statement or supplement the Final Prospectus to comply with the Act, the Company will promptly notify the Representative of such event and will promptly prepare and file with the Commission and furnish, at its own expense, to the Underwriters and the dealers and any other dealers upon request of the Representative, an amendment or supplement which will correct such statement or omission or an amendment which will effect such compliance. Neither the Representative’s consent to, nor the Underwriters’ delivery of, any such amendment or supplement shall constitute a waiver of any of the conditions set forth in Section 7 hereof.

(d)Rule 158. As soon as practicable, but not later than 16 months, after the date of this Agreement, the Company will make generally available to its security holders an earnings statement covering a period of at least 12 months beginning after the date of this Agreement and satisfying the provisions of Section 11(a) of the Act and Rule 158.

(e)Furnishing of Prospectuses. The Company will furnish to the Representative copies of the Registration Statement, including all exhibits, any Statutory Prospectus, the Final Prospectus and all amendments and supplements to such documents, in each case as soon as available and in such quantities as the Representative reasonably requests. The Company will pay the expenses of printing and distributing to the Underwriters all such documents.

(f)Blue Sky Qualifications. The Company will arrange for the qualification of the Offered Securities for sale under the laws of such jurisdictions as the Representative designates and will continue such qualifications in effect so long as required for the distribution.

(g)Reporting Requirements. During the period of five years hereafter, the Company will furnish to the Representative and, upon request, to each of the other Underwriters, as soon as practicable after the end of each fiscal year, a copy of its annual report to stockholders for such year; and the Company will furnish to the Representative (i) as soon as available, a copy of each report and any definitive proxy statement of the Company filed with the Commission under the Exchange Act or mailed to stockholders, and (ii) from time to time, such other information concerning the Company as the Representative may reasonably request. However, so long as the Company is subject to the reporting requirements of either Section 13 or Section 15(d) of the Exchange Act and is timely filing reports with the Commission on its Electronic Data Gathering, Analysis and Retrieval system (“EDGAR”), it is not required to furnish such reports or statements to the Underwriters.

(h)Payment of Expenses. The Company will pay all expenses incident to the performance of its obligations under this Agreement, including but not limited to any filing fees and other expenses (including fees and disbursements of counsel to the Underwriters) incurred in connection with qualification of the Offered Securities for sale under the laws of such jurisdictions as the Representative designates and the preparation and printing of memoranda relating thereto, any fees charged by investment rating agencies for the rating of the Offered Securities, fees and expenses of the Company’s

independent public or certified public accountants and other advisors, costs and expenses related to the review by FINRA of the Offered Securities (including filing fees and the fees and expenses of counsel for the Underwriters relating to such review), costs and expenses relating to investor presentations or any “road show” in connection with the offering and sale of the Offered Securities including, without limitation, any travel expenses of the Company’s officers and employees and any other expenses of the Company including the chartering of airplanes, fees and expenses incident to listing the Offered Securities on the New York Stock Exchange and other national and foreign exchanges, fees and expenses in connection with the registration of the Offered Securities under the Exchange Act, and expenses incurred in distributing preliminary prospectuses and the Final Prospectus (including any amendments and supplements thereto) to the Underwriters and for expenses incurred for preparing, printing and distributing any Issuer Free Writing Prospectuses to investors or prospective investors.

(i)Use of Proceeds. The Company will use the net proceeds received in connection with this offering in the manner described in the “Use of Proceeds” section of the General Disclosure Package and, except as disclosed in the General Disclosure Package, the Company does not intend to use any of the proceeds from the sale of the Offered Securities hereunder to repay any outstanding debt owed to any affiliate of any Underwriter.

(j)Absence of Manipulation. The Company will not take, directly or indirectly, any action designed to or that would constitute or that might reasonably be expected to cause or result in, stabilization or manipulation of the price of any securities of the Company to facilitate the sale or resale of the Offered Securities.

(k)Restriction on Sale of Securities. For the period specified below (the “Lock-Up Period”), the Company will not, directly or indirectly, take any of the following actions with respect to its shares of common stock or any securities convertible into or exchangeable or exercisable for any of its shares of common stock (“Lock-Up Securities”): (i) offer, sell, issue, contract to sell, pledge or otherwise dispose of Lock-Up Securities, (ii) offer, sell, issue, contract to sell, contract to purchase or grant any option, right or warrant to purchase Lock-Up Securities, (iii) enter into any swap, hedge or any other agreement that transfers, in whole or in part, the economic consequences of ownership of Lock-Up Securities, (iv) establish or increase a put equivalent position or liquidate or decrease a call equivalent position in Lock-Up Securities within the meaning of Section 16 of the Exchange Act or (v) file with the Commission a registration statement under the Act relating to Lock-Up Securities, or publicly disclose the intention to take any such action, without the prior written consent of the Representative, except grants of employee stock options pursuant to the terms of a plan in effect on the date hereof, issuances of Lock-Up Securities pursuant to the exercise of such options or the exercise of any other employee stock options outstanding on the date hereof or issuances of Lock-Up Securities pursuant to the Company’s dividend reinvestment and direct stock purchase plan, employee stock purchase plan, director and executive compensation plans (including deferred compensation plans) and other employee benefits plans and the grant of options or other equity awards under any such director and executive compensation plans. The initial Lock-Up Period will commence on the date hereof and continue for 90

days after the date hereof or such earlier date that the Representative consents to in writing; provided, however, that if (1) during the last 17 days of the initial Lock-Up Period, the Company releases earnings results or material news or a material event relating to the Company occurs or (2) prior to the expiration of the initial Lock-Up Period, the Company announces that it will release earnings results during the 16-day period beginning on the last day of the initial Lock-Up Period, then in each case the Lock-Up Period will be extended until the expiration of the 18-day period beginning on the date of release of the earnings results or the occurrence of the material news or material event, as applicable; provided that the foregoing proviso shall not apply if (i) the safe harbor provided by Rule 139 under the Act is available to the Representative in the manner contemplated by Rule 2711(f)(4) of the National Association of Securities Dealers, Inc. (“NASD”) or any successor provision or amendment thereto and (ii) within the 3 business days preceding the 15th calendar day before the last day of the restricted period, the Company delivers (in accordance with Section 11) to each of the Representative a certificate, signed by the Chief Financial Officer or Chief Executive Officer of the Company, certifying on behalf of the Company that the Offered Securities are “actively traded securities,” within the meaning of NASD Rule 2711(f)(4) or any successor provision or amendment thereto. The Company will provide the Representative with notice of any announcement described in clause (2) of the preceding sentence that gives rise to an extension of the Lock-Up Period.

6.Free Writing Prospectuses. The Company represents and agrees that, unless it obtains the prior consent of the Representative, and each Underwriter represents and agrees that, unless it obtains the prior consent of the Company and the Representative, it has not made and will not make any offer relating to the Offered Securities that would constitute an Issuer Free Writing Prospectus, or that would otherwise constitute a “free writing prospectus,” as defined in Rule 405, required to be filed with the Commission. Any such free writing prospectus consented to by the Company and the Representative is hereinafter referred to as a “Permitted Free Writing Prospectus.” The Company represents that it has treated and agrees that it will treat each Permitted Free Writing Prospectus as an “issuer free writing prospectus,” as defined in Rule 433, and has complied and will comply with the requirements of Rules 164 and 433 applicable to any Permitted Free Writing Prospectus, including timely Commission filing where required, legending and record keeping.

7.Conditions of the Obligations of the Underwriters. The obligations of the several Underwriters to purchase and pay for the Offered Securities on the Closing Date will be subject to the accuracy of the representations and warranties of the Company herein (as though made on the Closing Date), to the accuracy of the statements of Company officers made pursuant to the provisions hereof, to the performance by the Company of its obligations hereunder and to the following additional conditions precedent:

(a)Accountants’ Comfort Letters. The Representative shall have received letters, dated, respectively, the date hereof and the Closing Date, of Deloitte & Touche LLP confirming that they are a registered public accounting firm and independent public accountants within the meaning of the Securities Laws and containing such other information of the type ordinarily included in accounts’ “comfort letters” in form and substance satisfactory to the Representative, covering the financial information in the

Registration Statement, General Disclosure Package and the Final Prospectus and other customary matters.

(b)Filing of Prospectus. The Final Prospectus shall have been filed with the Commission in accordance with the Rules and Regulations and Section 5(a) hereof. No stop order suspending the effectiveness of the Registration Statement or of any part thereof shall have been issued and no proceedings for that purpose shall have been instituted or, to the knowledge of the Company, shall be contemplated by the Commission.

(c)No Material Adverse Change. Subsequent to the execution and delivery of this Agreement, there shall not have occurred (i) any change, or any development or event involving a prospective change, in the condition (financial or otherwise), results of operations, business, properties or prospects of the Company and its subsidiaries taken as a whole which, in the judgment of the Representative, is material and adverse and makes it impractical or inadvisable to market the Offered Securities; (ii) any downgrading in the rating of any debt securities of the Company by any “nationally recognized statistical rating organization” (as defined in Section 3(a)(62) of the Exchange Act), or any public announcement that any such organization has under surveillance or review its rating of any debt securities of the Company (other than an announcement with positive implications of a possible upgrading, and no implication of a possible downgrading, of such rating); (iii) any change in U.S. or international financial, political or economic conditions or currency exchange rates or exchange controls the effect of which is such as to make it, in the judgment of the Representative, impractical to market or to enforce contracts for the sale of the Offered Securities, whether in the primary market or in respect of dealings in the secondary market; (iv) any suspension or material limitation of trading in securities generally on the New York Stock Exchange, or any setting of minimum or maximum prices for trading on such exchange; (v) or any suspension of trading of any securities of the Company on any exchange or in the over-the-counter market; (vi) any banking moratorium declared by any U.S. federal or New York authorities; (vii) any major disruption of settlements of securities, payment, or clearance services in the United States or any other country where such securities are listed or (viii) any attack on, outbreak or escalation of hostilities or act of terrorism involving the United States, any declaration of war by Congress or any other national or international calamity or emergency if, in the judgment of the Representative, the effect of any such attack, outbreak, escalation, act, declaration, calamity or emergency is such as to make it impractical or inadvisable to market the Offered Securities or to enforce contracts for the sale of the Offered Securities.

(d)Opinion of Counsel for Company. The Representative shall have received an opinion, dated the Closing Date, of Jones Day, counsel for the Company, substantially in the form set forth in Exhibit B hereto. In addition, the Representative shall have received an opinion, dated the Closing Date, of Timothy P. Olson, senior corporate counsel and corporate secretary of the Company, substantially in the form set forth in Exhibit A hereto.

(e)Opinion of Counsel for Underwriters. The Representative shall have received from Hunton & Williams LLP, counsel for the Underwriters, such opinion or opinions, dated the Closing Date, with respect to such matters as the Representative may require, and the Company shall have furnished to such counsel such documents as they request for the purpose of enabling them to pass upon such matters.

(f)Officer’s Certificate. The Representative shall have received a certificate, dated the Closing Date, of an executive officer of the Company and a principal financial or accounting officer of the Company in which such officers shall state that: the representations and warranties of the Company in this Agreement are true and correct; the Company has complied with all agreements and satisfied all conditions on its part to be performed or satisfied hereunder at or prior to the Closing Date; no stop order suspending the effectiveness of the Registration Statement has been issued and no proceedings for that purpose have been instituted or, to the best of their knowledge and after reasonable investigation, are contemplated by the Commission; and, subsequent to the date of the most recent financial statements in the General Disclosure Package and the Final Prospectus, there has been no material adverse change in the condition (financial or otherwise), results of operations, business, properties or prospects of the Company and its subsidiaries taken as a whole except as set forth in the General Disclosure Package and the Final Prospectus.

(g)Lock-up Agreements. On or prior to the date hereof, the Representative shall have received lock-up letters from each of the executive officers and directors of the Company listed in Exhibit C-1 hereto, in each case substantially in the form of Exhibit C-2 hereto.

The Company will furnish the Representative with such conformed copies of such opinions, certificates, letters and documents as the Representative reasonably requests. The Representative may waive on behalf of the Underwriters compliance with any conditions to the obligations of the Underwriters hereunder.

8.Indemnification and Contribution.

(a)Indemnification of Underwriters. The Company will indemnify and hold harmless each Underwriter, its partners, members, directors, officers, employees, agents, affiliates and each person, if any, who controls such Underwriter within the meaning of Section 15 of the Act or Section 20 of the Exchange Act (each, an “Indemnified Party”), against any and all losses, claims, damages or liabilities, joint or several, to which such Indemnified Party may become subject, under the Act, the Exchange Act, other Federal or state statutory law or regulation or otherwise, insofar as such losses, claims, damages or liabilities (or actions in respect thereof) arise out of or are based upon (i) any untrue statement or alleged untrue statement of any material fact contained in any part of the Registration Statement at any time or are based upon the omission or alleged omission of a material fact required to be stated therein or necessary to make the statements therein not misleading, or (ii) any untrue statement or alleged untrue statement of any material fact contained in any Statutory Prospectus as of any time, the Final Prospectus or any Issuer Free Writing Prospectus, or arise out of or are based upon the omission or alleged omission of a material fact required to be stated therein or necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading, and, in each case, will reimburse each Indemnified Party for any legal or other expenses reasonably incurred by such Indemnified Party in connection with investigating or defending against any loss, claim, damage, liability, action, litigation, investigation or proceeding whatsoever (whether or not such Indemnified Party is a party thereto), whether threatened or commenced, and in connection with the enforcement of this provision with respect to any of the above as such expenses are incurred; provided, however, that the Company will not be liable in any such case to the extent that any such loss, claim, damage or liability arises out of or is based upon an untrue statement or

alleged untrue statement in or omission or alleged omission from any of such documents in reliance upon and in conformity with written information furnished to the Company by any Underwriter through the Representative specifically for use therein, it being understood and agreed that the only such information furnished by any Underwriter consists of the information described as such in subsection (b) below.

(b)Indemnification of Company. Each Underwriter will severally and not jointly indemnify and hold harmless the Company, each of its directors and each of its officers who signs a Registration Statement and each person, if any, who controls the Company within the meaning of Section 15 of the Act or Section 20 of the Exchange Act (each, an “Underwriter Indemnified Party”), against any losses, claims, damages or liabilities to which such Underwriter Indemnified Party may become subject, under the Act, the Exchange Act, other Federal or state statutory law or regulation or otherwise, insofar as such losses, claims, damages or liabilities (or actions in respect thereof) arise out of or are based upon (i) any untrue statement or alleged untrue statement of any material fact contained in any part of the Registration Statement at any time or are based upon the omission or alleged omission of a material fact required to be stated therein or necessary to make the statements therein not misleading, or (ii) any untrue statement or alleged untrue statement of any material fact contained in any Statutory Prospectus as of any time, the Final Prospectus or any Issuer Free Writing Prospectus, or arise out of or are based upon the omission or alleged omission of a material fact required to be stated therein or necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading, in each case to the extent, but only to the extent, that such untrue statement or alleged untrue statement or omission or alleged omission was made in reliance upon and in conformity with written information furnished to the Company by such Underwriter through the Representative specifically for use therein, and will reimburse any legal or other expenses reasonably incurred by such Underwriter Indemnified Party in connection with investigating or defending against any such loss, claim, damage, liability, action, litigation, investigation or proceeding whatsoever (whether or not such Underwriter Indemnified Party is a party thereto), whether threatened or commenced, based upon any such untrue statement or omission, or any such alleged untrue statement or omission as such expenses are incurred, it being understood and agreed that the only such information furnished by any Underwriter consists of the following information in the Final Prospectus furnished on behalf of each Underwriter: the information relating to stabilizing transactions and short sales contained in the ninth and tenth paragraphs under the caption “Underwriting.”

(c)Actions against Parties; Notification. Promptly after receipt by an indemnified party under this Section of notice of the commencement of any action, such indemnified party will, if a claim in respect thereof is to be made against the indemnifying party under subsection (a) or (b) above, notify the indemnifying party of the commencement thereof; but the failure to notify the indemnifying party shall not relieve it from any liability that it may have under subsection (a) or (b) above except to the extent that it has been materially prejudiced (through the forfeiture of substantive rights or defenses) by such failure; and provided further that the failure to notify the indemnifying party shall not relieve it from any liability that it may have to an indemnified party otherwise than under subsection (a) or (b) above. In case any such action is brought against any indemnified party and it notifies the indemnifying party of the commencement thereof, the indemnifying party will be entitled to participate therein and, to the extent that it may wish, jointly with any other indemnifying party similarly notified, to assume the defense thereof, with counsel reasonably satisfactory to such indemnified party (who shall not, except with the consent of the indemnified party, be counsel to the indemnifying party), and after notice from the indemnifying party to such indemnified party of its election so to assume the defense thereof, the indemnifying party will not be liable to such indemnified party under this Section for any legal or other expenses subsequently incurred by such indemnified party in connection with the defense thereof other than reasonable costs of investigation. No indemnifying party shall, without the prior written consent of the indemnified party, effect any settlement of any pending or threatened action in respect of which any indemnified party is or could have been a party and indemnity could have been sought hereunder by such indemnified party unless such settlement (i) includes an unconditional release of such indemnified party from all liability on any claims that are the subject matter of such action and (ii) does not include a statement as to, or an admission of, fault, culpability or a failure to act by or on behalf of an indemnified party.

(d)Contribution. If the indemnification provided for in this Section is unavailable or insufficient to hold harmless an indemnified party under subsection (a) or (b) above, then each indemnifying party shall contribute to the amount paid or payable by such indemnified party as a result of the losses, claims, damages or liabilities referred to in subsection (a) or (b) above (i) in such proportion as is appropriate to reflect the relative benefits received by the Company on the one hand and the Underwriters on the other from the offering of the Offered Securities or (ii) if the allocation provided by clause (i) above is not permitted by applicable law, in such proportion as is appropriate to reflect not only the relative benefits referred to in clause (i) above but also the relative fault of the Company on the one hand and the Underwriters on the other in connection with the statements or omissions which resulted in such losses, claims, damages or liabilities as well as any other relevant equitable considerations. The relative benefits received by the Company on the one hand and the Underwriters on the other shall be deemed to be in the same proportion as the total net proceeds from the offering (before deducting expenses) received by the Company bear to the total compensation received by the Underwriters. The relative fault shall be determined by reference to, among other things, whether the untrue or alleged untrue statement of a material fact or the omission or alleged omission to state a material fact relates to information supplied by the Company or the Underwriters and the parties’ relative intent, knowledge, access to information and

opportunity to correct or prevent such untrue statement or omission. The amount paid by an indemnified party as a result of the losses, claims, damages or liabilities referred to in the first sentence of this subsection (d) shall be deemed to include any legal or other expenses reasonably incurred by such indemnified party in connection with investigating or defending any action or claim which is the subject of this subsection (d). Notwithstanding the provisions of this subsection (d), the Underwriters shall not be required to contribute any amount in excess of compensation received by them under this Agreement. No person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Act) shall be entitled to contribution from any person who was not guilty of such fraudulent misrepresentation. The Underwriters’ obligations in this subsection (d) to contribute are several in proportion to their respective underwriting obligations and not joint. The Company and the Underwriters agree that it would not be just and equitable if contribution pursuant to this Section 8(d) were determined by pro rata allocation (even if the Underwriters were treated as one entity for such purpose) or by any other method of allocation which does not take account of the equitable considerations referred to in this Section 8(d).

9.Default of Underwriters. If any Underwriter or Underwriters default in their obligations to purchase Offered Securities hereunder on the Closing Date and the aggregate number of Offered Securities that such defaulting Underwriter or Underwriters agreed but failed to purchase does not exceed 10% of the total number of Offered Securities that the Underwriters are obligated to purchase on the Closing Date, the Representative may make arrangements satisfactory to the Company for the purchase of such Offered Securities by other persons, including any of the Underwriters, but if no such arrangements are made by the Closing Date, the non-defaulting Underwriters shall be obligated severally, in proportion to their respective commitments hereunder, to purchase the Offered Securities that such defaulting Underwriters agreed but failed to purchase on the Closing Date. If any Underwriter or Underwriters so default and the aggregate number of Offered Securities with respect to which such default or defaults occur exceeds 10% of the total number of Offered Securities that the Underwriters are obligated to purchase on the Closing Date and arrangements satisfactory to the Representative and the Company for the purchase of such Offered Securities by other persons are not made within 36 hours after such default, this Agreement will terminate without liability on the part of any non-defaulting Underwriter or the Company, except as provided in Section 10. As used in this Agreement, the term “Underwriter” includes any person substituted for an Underwriter under this Section. Nothing herein will relieve a defaulting Underwriter from liability for its default.

10.Survival of Certain Representations and Obligations. The respective indemnities, agreements, representations, warranties and other statements of the Company or its officers and of the several Underwriters set forth in or made pursuant to this Agreement will remain in full force and effect, regardless of any investigation, or statement as to the results thereof, made by or on behalf of any Underwriter, the Company or any of their respective representatives, officers or directors or any controlling person, and will survive delivery of and payment for the Offered Securities. If the purchase of the Offered Securities by the Underwriters is not consummated for any reason, the Company will reimburse the Underwriters for all out-of-pocket expenses (including fees and disbursements of counsel) reasonably incurred by them in connection with the offering of the Offered Securities, except for any Underwriter or Underwriters that defaulted in their obligations to purchase Offered Securities hereunder on the Closing Date. If the

purchase of the Offered Securities by the Underwriters is not consummated for any reason, Sections 5(h), 8 and 16 hereof shall remain in effect. In addition, if any Offered Securities have been purchased hereunder, the representations and warranties in Section 2 and all obligations under Section 5 shall also remain in effect.

11.Notices. All communications hereunder will be in writing and, if sent to the Underwriters, will be mailed, delivered or telegraphed and confirmed to the Representative c/o RBC Capital Markets, LLC, Three World Financial Center, 200 Vesey Street, 8^th Floor, New York, New York 10281, Attention: Equity Syndicate (phone: (877) 822-4089, e-mail: ***@***), or, if sent to the Company, will be mailed, delivered or telegraphed and confirmed to it at NorthWestern Corporation, 3010 West 69th Street, Sioux Falls, South Dakota 57108, Attention: Brian B. Bird, Chief Financial Officer (fax: (605) 978-2840); provided, however, that any notice to an Underwriter pursuant to Section 8 will be mailed, delivered or telegraphed and confirmed to such Underwriter.

12.Successors. This Agreement will inure to the benefit of and be binding upon the parties hereto and their respective successors and the officers and directors and controlling persons referred to in Section 8, and no other person will have any right or obligation hereunder.

13.Representation of Underwriters. The Representative will act for the several Underwriters in connection with this financing, and any action under this Agreement taken by the Representative jointly will be binding upon all the Underwriters.

14.Counterparts. This Agreement may be executed in any number of counterparts, each of which shall be deemed to be an original, but all such counterparts shall together constitute one and the same Agreement.

15.Absence of Fiduciary Relationship. The Company acknowledges and agrees that:

(a)No Other Relationship. The Representative has been retained solely to act as underwriters in connection with the sale of Offered Securities and that no fiduciary, advisory or agency relationship between the Company and the Representative has been created in respect of any of the transactions contemplated by this Agreement or the Final Prospectus, irrespective of whether the Representative has advised or is advising the Company on other matters;

(b)Arms’ Length Negotiations. The price of the Offered Securities set forth in this Agreement was established by the Company following discussions and arms-length negotiations with the Representative and the Company is capable of evaluating and understanding and understands and accepts the terms, risks and conditions of the transactions contemplated by this Agreement;

(c)Absence of Obligation to Disclose. The Company has been advised that the Representative and its affiliates are engaged in a broad range of transactions which may involve interests that differ from those of the Company and that the Representative has no obligation to disclose such interests and transactions to the Company by virtue of any fiduciary, advisory or agency relationship; and

(d)Waiver. The Company waives, to the fullest extent permitted by law, any claims it may have against the Representative for breach of fiduciary duty or alleged breach of fiduciary duty and agrees that the Representative shall have no liability (whether direct or indirect) to the Company in respect of such a fiduciary duty claim or to any person asserting a fiduciary duty claim on behalf of or in right of the Company, including stockholders, employees or creditors of the Company.

The Company hereby submits to the non-exclusive jurisdiction of the Federal and state courts in the Borough of Manhattan in The City of New York in any suit or proceeding arising out of or relating to this Agreement or the transactions contemplated hereby. The Company irrevocably and unconditionally waives any objection to the laying of venue of any suit or proceeding arising out of or relating to this Agreement or the transactions contemplated hereby in Federal and state courts in the Borough of Manhattan in The City of New York and irrevocably and unconditionally waives and agrees not to plead or claim in any such court that any such suit or proceeding in any such court has been brought in an inconvenient forum.

If the foregoing is in accordance with the Representative’s understanding of our agreement, kindly sign and return to the Company one of the counterparts hereof, whereupon it will become a binding agreement between the Company and the several Underwriters in accordance with its terms.

The foregoing Underwriting Agreement is hereby confirmed and accepted as of the date first above written.

Acting on behalf of itself and as the Representative of the several Underwriters

We have participated in the preparation of the Company’s registration statement on Form S-3 (Registration No. 333-202126) (the “Registration Statement”), the prospectus dated February 17, 2015 (the “Base Prospectus”), the preliminary prospectus supplement dated September 29, 2015 (together with the Base Prospectus, the “Preliminary Prospectus”), and the information relating to the Offered Securities contained in Schedule B-1 to the Underwriting Agreement (together with the Preliminary Prospectus, the “General Disclosure Package”) and the prospectus supplement, dated September 29, 2015 (together with the Base Prospectus, the “Final Prospectus”). Each of the Registration Statement, the General Disclosure Package and the Final Prospectus includes the documents incorporated or deemed incorporated by reference therein pursuant to Item 12 of Form S-3 under the Securities Act of 1933, as amended (the “Securities Act”). From time to time, we have had discussions with certain officers, directors and employees of the Company, with representatives of Deloitte & Touche LLP, the independent registered public accounting firm who examined the financial statements of the Company included or incorporated by reference in the Registration Statement, the General Disclosure Package and the Final Prospectus, with the Underwriters and with counsel to the Underwriters concerning the information contained or incorporated by reference in the Registration Statement, the General Disclosure Package and the Final Prospectus and the responses to various items in Form S-3. Based upon our participation and discussions described above, we are of the view that the Registration Statement (including all information deemed to be part of and included therein pursuant to Rule 430B under the Securities Act), as of September 29, 2015, which is the date you have identified as the earlier of the date the Final Prospectus was first used or the date of the first contract of sale of any Offered Securities (such date, the “Effective Date”), and the Final Prospectus, as of its date, complied as to form in all material respects with the requirements of the Securities Act and the rules and regulations of the Securities and Exchange Commission (the “Commission”) thereunder, except that we express no view with respect to the financial statements and reports relating thereto, financial schedules and other financial and statistical data included or incorporated by reference therein or excluded therefrom.

NorthWestern Corporation

3010 West 69th Street

Sioux Falls, SD 57108

RBC Capital Markets, LLC

Three World Financial Center, 8th Floor

200 Vesey Street

New York, New York 10281-8098

As Representative of the Several Underwriters

Dear Sirs:

As an inducement to the Underwriters to execute the Underwriting Agreement (the “Underwriting Agreement”), pursuant to which an offering will be made that is intended to result in an orderly market for the common stock, $0.01 par value per share (the “Securities”) of NorthWestern Corporation, and any successor (by merger or otherwise) thereto, (the “Company”), the undersigned hereby agrees that during the period specified in the following paragraph (the “Lock-Up Period”), the undersigned will not offer, sell, contract to sell, pledge or otherwise dispose of, directly or indirectly, any Securities or securities convertible into or exchangeable or exercisable for any Securities, enter into a transaction which would have the same effect, or enter into any swap, hedge or other arrangement that transfers, in whole or in part, any of the economic consequences of ownership of the Securities, whether any such aforementioned transaction is to be settled by delivery of the Securities or such other securities, in cash or otherwise, or publicly disclose the intention to make any such offer, sale, pledge or disposition, or to enter into any such transaction, swap, hedge or other arrangement, without, in each case, the prior written consent of RBC Capital Markets, LLC, as representative of the several underwriters (the “Representative”). In addition, the undersigned agrees that, without the prior written consent of the Representative, it will not, during the Lock-Up Period, make any demand for or exercise any right with respect to, the registration of any Securities or any security convertible into or exercisable or exchangeable for the Securities.

The initial Lock-Up Period will commence on the date of this Lock-Up Agreement and continue and include the date 90 days after the public offering date set forth on the final prospectus used to sell the Securities (the “Public Offering Date”) pursuant to the Underwriting Agreement, to which you are or expect to become parties; provided, however, that if (1) during the last 17 days of the initial Lock-Up Period, the Company releases earnings results or material news or a material event relating to the Company occurs or (2) prior to the expiration of the initial Lock-Up Period, the Company announces that it will release earnings results during the 16-day period beginning on the last day of the initial Lock-Up Period, then in each case the Lock-Up Period will be extended until the expiration of the 18-day period beginning on the date of release of the earnings results or the occurrence of the material news or material event, as applicable; provided that this sentence shall not apply if (i) the safe harbor provided by Rule 139 under the Securities Act of 1933, as amended, is available in the manner contemplated by Rule 2711(f)(4) of the National Association of Securities Dealers, Inc. (“NASD”) or any successor provision or amendment thereto and (ii) within the 3 business days preceding the 15th calendar day before the last day of the restricted period, the Company delivers (in accordance with Section 11 of the Underwriting Agreement) to each of the Representative a certificate, signed by the Chief Financial Officer or Chief Executive Officer of the Company, certifying on behalf of the Company that the Securities are “actively traded securities,” within the meaning of NASD Rule 2711(f)(4) or any successor provision or amendment thereto. The Company will provide the Representative with notice of any announcement described in clause (2) of the preceding sentence that gives rise to an extension of the Lock-Up Period.

The undersigned agrees that, prior to engaging in any transaction or taking any other action that is subject to the terms of this Lock-Up Agreement during the period from the date of this Lock-Up Agreement to and including the 34th day following the expiration of the initial Lock-Up Period, it will give notice thereof to the Company and will not consummate such transaction or take any such action unless it has received written confirmation from the Company that the Lock-Up Period (as may have been extended pursuant to the previous paragraph) has expired.

Any Securities received upon exercise of options granted to the undersigned will also be subject to this Lock-Up Agreement. Any Securities acquired by the undersigned in the open market will not be subject to this Lock-Up Agreement. A transfer of Securities to a family member or trust may be made, provided the transferee agrees to be bound in writing by the terms of this Lock-Up Agreement prior to such transfer, such transfer shall not involve a disposition for value and no filing by any party (donor, donee, transferor or transferee) under the Securities Exchange Act of 1934, as amended, shall be required or shall be voluntarily made in connection with such transfer (other than a filing on a Form 5 made after the expiration of the Lock-Up Period).

In furtherance of the foregoing, the Company and its transfer agent and registrar are hereby authorized to decline to make any transfer of shares of Securities if such transfer would constitute a violation or breach of this Lock-Up Agreement.

If the undersigned is an officer or director of the Company, the undersigned further agrees that the foregoing restrictions in this Lock-Up Agreement shall be equally applicable to any issuer-directed Securities the undersigned may purchase in the above-referenced offering.

If the undersigned is an officer or director of the Company, (i) the Representative agrees that, at least three business days before the effective date of any release or waiver of the foregoing restrictions in connection with a transfer of Securities, the Representative will notify the Company of the impending release or waiver, and (ii) the Company has agreed in the Underwriting Agreement to announce the impending release or waiver by press release through a major news service at least two business days before the effective date of the release or waiver. Any release or waiver granted by the Representative hereunder to any such officer or director shall only be effective two business days after the publication date of such press release. The provisions of this paragraph will not apply if (a) the release or waiver is effected solely to permit a transfer not for consideration and (b) the transferee has agreed in writing to be bound by the same terms described in this Lock-Up Agreement to the extent and for the duration that such terms remain in effect at the time of the transfer.

This Lock-Up Agreement shall be binding on the undersigned and the successors, heirs, personal representatives and assigns of the undersigned. This agreement shall be governed by, and construed in accordance with, the laws of the State of New York.

        

Very truly yours,

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