Company: PRTA
Filing Date: 2025-10-07
Form Type: DEF 14A
Source: 0001140361-25-037500
Chunk: 1

Company: PROTHENA CORP PUBLIC LTD CO
Filing Date: 2025-10-07
Form: DEF 14A
Chunk 1
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 exercise your right. Sincerely,

| Daniel G. Welch    
 Chair of the Board |     | Gene G. Kinney Ph.D.                            
 President and Chief Executive Officer, Director |

This Proxy Statement and the enclosed proxy card are being made available to shareholders on or about October 7, 2025.

TABLE OF CONTENTS

| PROTHENA CORPORATION PLC |

Registered in Ireland - No. 518146 77 Sir John Rogerson’s Quay, Block C, Grand Canal Docklands, Dublin 2, D02 VK60, Ireland NOTICE OF EXTRAORDINARY GENERAL MEETING OF SHAREHOLDERS TO BE HELD ON NOVEMBER 19, 2025 To the Shareholders of Prothena Corporation plc: NOTICE IS HEREBY GIVEN that an Extraordinary General Meeting of Shareholders (the “EGM”) of Prothena Corporation plc, an Irish public limited company (the “Company”), will be held on Wednesday, November 19, 2025, at 4:00 p.m. local time, at the offices of the Company’s legal counsel, A&L Goodbody LLP, 25 North Wall Quay, Dublin 1, D01 H104, Ireland, for the following purposes:

| 1. | To approve the reduction of Company capital to facilitate the creation of distributable reserves; and |

| 2. | To transact such other business as may properly come before the EGM or any adjournment or postponement thereof. |

The text of Proposal No.1 is set out in the Proxy Statement accompanying this Notice. Pursuant to our Constitution and Irish law, Proposal No. 1 is being proposes as a special resolution requiring the approval of at least 75% of the votes cast at the EGM. Only shareholders who owned our ordinary shares at the close of business on September 24, 2025, may vote at the EGM. Each shareholder of record will be entitled to one vote per ordinary share on each matter submitted to a vote of the shareholders, as long as those shares are represented at the EGM, either in person or by proxy. Shareholders who are entitled to attend and vote at the EGM are entitled to appoint a proxy or proxies to attend and vote on their behalf at the EGM; such proxy is not required to be a shareholder of the Company. Our Board of Directors unanimously recommends that you vote FOR the approval of the reduction of the Company’s capital to facilitate the creation of distributable reserves, as described in Proposal