WILLIS TOWERS WATSON PUBLIC LIMITED COMPANY, as Issuer WILLISTOWERS WATSON SUB HOLDINGS UNLIMITED WILLIS NETHERLANDS HOLDINGS B.V. WILLIS INVESTMENT UK HOLDINGS LIMITED TA I LIMITED WTWBERMUDA HOLDINGS LTD. TRINITY ACQUISITION PLC (f/k/a TRINITY ACQUISITION LIMITED) WILLIS GROUP LIMITED and WILLIS NORTH AMERICA INC., as Existing Guarantors and WTW UK HOLDINGSLIMITED as Assuming Guarantor and THE BANK OF NEWYORK MELLON, as Trustee ThirdSupplemental Indenture Dated as of August 11, 2017 to the Indenture dated as of March 17, 2011, as amended and supplemented by the First Supplemental Indenture dated as of March 17, 2011 and the SecondSupplemental Indenture dated as of March 9, 2016. Providing forthe Assumption of Guaranteed Obligations THIRD SUPPLEMENTAL INDENTURE

Exhibit 4.2

WILLIS TOWERS WATSON PUBLIC LIMITED COMPANY,

as Issuer

WILLIS TOWERS WATSON SUB HOLDINGS UNLIMITED

WILLIS NETHERLANDS HOLDINGS B.V.

WILLIS INVESTMENT UK HOLDINGS LIMITED

TA I LIMITED

WTW BERMUDA HOLDINGS LTD.

TRINITY ACQUISITION PLC (f/k/a TRINITY ACQUISITION LIMITED)

WILLIS GROUP LIMITED and

WILLIS NORTH AMERICA INC.,

as Existing Guarantors

and

WTW UK HOLDINGS LIMITED

as Assuming Guarantor

and

THE BANK OF NEW YORK MELLON,

as Trustee

Third Supplemental Indenture

Dated as of August 11, 2017

to the Indenture dated as of March 17, 2011,

as amended and supplemented by

the First Supplemental Indenture dated as of March 17, 2011

and

the Second Supplemental Indenture dated as of March 9, 2016.

Providing for the Assumption of Guaranteed Obligations

THIRD SUPPLEMENTAL INDENTURE

THIRD SUPPLEMENTAL INDENTURE (this “Third Supplemental Indenture”), dated August 11, 2017, Willis Towers Watson Public Limited Company (f/k/a Willis Group Holdings Public Limited Company), a company organized and existing under the laws of Ireland, as issuer (the “Issuer”), the Guarantors listed on Schedule A, attached hereto (the “Existing Guarantors”), Willis Towers Watson UK Holdings Limited, a company incorporated under the laws of England and Wales (the “Assuming Guarantor”), and The Bank of New York Mellon, a New York banking corporation, as trustee (the “Trustee”), to the Indenture, dated as of March 17, 2011, among the Issuer, the Existing Guarantors and the Trustee (the “Base Indenture”), as amended and supplemented by the First Supplemental Indenture, dated as of March 17, 2011 (the “First Supplemental Indenture”), and the Second Supplemental Indenture dated as of March 9, 2016 (the “Second Supplemental Indenture” and together with the First Supplemental Indenture and the Base Indenture, the “Indenture”).

RECITALS:

WHEREAS, the Issuer, the Existing Guarantors and the Trustee have heretofore entered into the Indenture to provide for the issuance of the Issuer’s unsecured senior debentures, notes or other evidences of Indebtedness (the “Securities”);

WHEREAS, Section 9.01 of the Indenture permits a Guarantor (this and other capitalized terms used herein and not otherwise defined have the meanings given to them in the Base Indenture) to convey, transfer or lease its properties and assets substantially as an entirety to any Person, provided that, (a) except in the case of Willis North America Inc., the successor Person shall be a Person organized and existing under the laws of, inter alia, England and Wales, and such Person shall expressly assume by supplemental indenture, all the obligations of such Guarantor under the Indenture and the Securities and immediately after such transaction no Event of Default shall have happened or be continuing and (b) the Issuer has delivered to the Trustee an Officers’ Certificate and an Opinion of Counsel, each stating that such conveyance, transfer or lease and supplemental indenture comply with Article Nine of the Indenture and all the conditions precedent stated therein have been complied with;

WHEREAS, Section 9.02 of the Indenture permits the predecessor corporation to be relieved of all obligations and covenants under the Indenture and the Securities after the conveyance or transfer of the properties and assets of such Guarantor substantially as an entirety in accordance with Section 9.01 and after the successor Person succeeds to, is substituted for, and becomes entitled to exercise every right and power of such Guarantor;

WHEREAS, Section 10.01(1) of the Indenture permits the Issuer, the Guarantors and the Trustee to enter into a supplemental indenture to the Indenture without the consent of the Holders of the Securities to evidence the succession of another Person to a Guarantor and the assumption by such successor Person of the covenants of the Guarantor in the Indenture and the Securities pursuant to Article Nine of the Indenture;

WHEREAS, the properties and assets of WTW Bermuda Holdings Limited (the “Transferring Guarantor”) are being transferred substantially as an entirety to the Assuming Guarantor (the “Transfer”) and the Assuming Guarantor desires to assume all of the Guaranteed Obligations of the Transferring Guarantor, including all obligations of a Guarantor under Article Sixteen of the Indenture;

WHEREAS, the Trustee has agreed to enter into this Third Supplemental Indenture to evidence the foregoing assumptions;

WHEREAS, the Trustee has received an Opinion of Counsel and an Officers’ Certificate, pursuant to Sections 1.02, 9.01 and 10.03 of the Indenture, stating, as applicable, that (a) the execution of the Third Supplemental Indenture is authorized or permitted by the Indenture, (b) the transfer of the Transferring Guarantor’s properties and assets substantially as an entirety to the Assuming Guarantor and the Third Supplemental Indenture comply with Article Nine of the Indenture and (c) all conditions precedent (including any covenants compliance with which constitutes a condition precedent) provided for in the Indenture to such transaction and to the execution and delivery by the Trustee of the Third Supplemental Indenture have been complied with;

WHEREAS the Trustee has received a Board Resolution of the Issuer and a resolution of the board of directors of the Existing Guarantors and of the Assuming Guarantor each authorizing the entering into of this Third Supplemental Indenture;

WHEREAS the Trustee is authorized to enter into this Third Supplemental Indenture and the Issuer has requested and hereby requests that the Trustee join with the Issuer, the Existing Guarantors and the Assuming Guarantor in entering into this Third Supplemental Indenture; and

WHEREAS, all things necessary to make this Third Supplemental Indenture a valid agreement of the Issuer, the Assuming Guarantor, the Existing Guarantors and the Trustee, in accordance with its terms, have been done.

NOW, THEREFORE, in consideration of the above premises, each party covenants and agrees, for the benefit of the other parties and for the equal and ratable benefit of all of the Holders of the Securities, as follows:

ARTICLE ONE

ASSUMPTION OF GUARANTOR OBLIGATIONS

Section 1.1    Assumption of Guarantor Obligations by Assuming Guarantor.

Upon consummation of the Transfer, the Assuming Guarantor hereby assumes the Guaranteed Obligations of the Transferring Guarantor under the Indenture and the Securities, and thereby and hereby becomes, and agrees to be bound by all of the provisions of the Indenture (including Article Ten thereof) applicable to, a Guarantor, as if originally named as a guarantor in the Base Indenture. Upon consummation of the Transfer, the Transferring Guarantor is hereby relieved of all obligations and covenants under the Indenture and the Securities pursuant to Section 9.02 of the Indenture.

ARTICLE TWO

MISCELLANEOUS

Section 2.1    Integral Part.

This Third Supplemental Indenture constitutes an integral part of the Indenture.

Section 2.2    Adoption, Ratification and Confirmation.

The Indenture, as supplemented and amended by this Third Supplemental Indenture, is in all respects hereby adopted, ratified and confirmed, and this Third Supplemental Indenture shall be deemed part of the Indenture in the manner and to the extent herein and therein provided. The provisions of this Third Supplemental Indenture shall, subject to the terms hereof, supersede the provisions of the Indenture to the extent the Indenture is inconsistent herewith.

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Section 2.3    Counterparts.

This Third Supplemental Indenture may be executed in any number of counterparts, each of which so executed shall be deemed to be an original, but all such counterparts shall together constitute but one and the same instrument. The exchange of copies of this Third Supplemental Indenture and of signature pages by facsimile or PDF transmission shall constitute effective execution and delivery of this Third Supplemental Indenture as to the parties hereto and may be used in lieu of the original Supplemental Indenture for all purposes. Signatures of the parties hereto transmitted by facsimile or PDF shall be deemed to be their original signatures for all purposes.

Section 2.4    Governing Law.

THIS THIRD SUPPLEMENTAL INDENTURE SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK, WITHOUT GIVING EFFECT TO APPLICABLE PRINCIPLES OF CONFLICTS LAW. EACH OF THE ISSUER, THE EXISTING GUARANTORS, THE ASSUMING GUARANTOR AND THE TRUSTEE IRREVOCABLY WAIVES, TO THE FULLEST EXTENT PERMITTED BY APPLICABLE LAW, ANY AND ALL RIGHT TO TRIAL BY JURY IN ANY LEGAL PROCEEDING ARISING OUT OF OR RELATING TO THIS THIRD SUPPLEMENTAL INDENTURE OR THE TRANSACTIONS CONTEMPLATED HEREBY.

Section 2.5    Conflict with Trust Indenture Act.

If and to the extent that any provision of the Indenture or this Third Supplemental Indenture limits, qualifies or conflicts with a provision required under the terms of the Trust Indenture Act, the Trust Indenture Act provision shall control.

Section 2.6 Effect of Heading.

The Article and Section headings herein are for convenience only and shall not affect the construction hereof.

Section 2.7 Separability Clause.

In case any provision in the Indenture, this Third Supplemental Indenture or in the Securities shall be invalid, illegal or unenforceable, the validity, legality and enforceability of the remaining provisions shall not in any way be affected or impaired thereby.

Section 2.8 Successors and Assigns.

All covenants and agreements in the Indenture and this Third Supplemental Indenture by the parties hereto shall bind their respective successors and assigns, whether so expressed or not.

Section 2.9 Benefit of Indenture.

Nothing in the Indenture or this Third Supplemental Indenture or in the Securities, express or implied, shall give to any Person, other than the parties hereto, any Security Registrar, any Paying Agent, and their successors hereunder, and the Holders of the Securities, any benefit or any legal or equitable right, remedy or claim hereunder or under the Indenture.

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Section 2.10 The Trustee.

The Trustee shall not be responsible in any manner whatsoever for or in respect of the validity or, sufficiency or adequacy of this Third Supplemental Indenture or for or in respect of the statements or recitals contained herein, all of which are made solely by the Issuer, the Assuming Guarantor, and the Existing Guarantors and the Trustee assumes no responsibility for their correctness.

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IN WITNESS WHEREOF, the parties hereto have caused this Third Supplemental Indenture to be duly executed, all as of the day and year first written above.

[Signature Page to the 3rd Supplemental Indenture to the 2011 Indenture (Parent)]

[Signature Page to the 3rd Supplemental Indenture to the 2011 Indenture (Parent)]

[Signature Page to the 3rd Supplemental Indenture to the 2011 Indenture (Parent)]

[Signature Page to the 3rd Supplemental Indenture to the 2011 Indenture (Parent)]

[Signature Page to the 3rd Supplemental Indenture to the 2011 Indenture (Parent)]

[Signature Page to the 3rd Supplemental Indenture to the 2011 Indenture (Parent)]

SCHEDULE A

EXISTING GUARANTORS

A-1