Prothena Biosciences Inc 650 Gateway Boulevard South San Francisco, CA 94010 U.S.A.

We have requested that you continue to serve as Chief Medical Officer of Prothena Corporation plc and continue your employment with the Company until we hire and appoint a new Chief Medical Officer. You have agreed to do so.

We have requested that you continue your employment with the Company after a new Chief Medical Officer is hired and appointed until December 31, 2017 (the “Transition Period”), to assist with the transition of your responsibilities and other matters as requested by your replacement or me. During the first three months of the Transition Period, we have asked that you remain a full-time employee; thereafter until December 31, 2017, we have asked that you remain as a part-time employee regularly working no less than 30 hours per week. You have agreed to do so.

For so long as you continue to serve as Chief Medical Officer, you will continue to receive the same compensation and participate in the same compensation and benefit plans and arrangements that you currently receive and in which you currently participate; provided that you will not be eligible to receive a bonus for 2017.

During the portion of the Transition Period that you remain a full-time employee, you will continue to be paid a salary at your current annual salary rate of $371,315. During the portion of the Transition Period that you remain a part-time employee, you will be paid a salary at an annual salary rate of $278,486. While you remain an employee, you will continue to be eligible to participate in benefit plans and arrangements generally available to other full-time or part-time employees (as the case may be); provided that you will not be eligible to receive a cash bonus for 2017. Stock options previously granted to you will continue to vest in accordance with their terms while you remain an employee. In according with their terms, any options that are unvested on the date that you cease employment with the Company will immediately terminate, and any options that are vested on that date will remain outstanding until the three-month anniversary of the date your employment ends.