Company: PRTA
Filing Date: 2025-03-28
Form Type: DEF 14A
Source: 0001559053-25-000017
Chunk: 53

Company: PROTHENA CORP PUBLIC LTD CO
Filing Date: 2025-03-28
Form: DEF 14A
Chunk 53
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 |      — |     |               |         — |     |                |     — |
| All employees, including all current officers who are not executive officers, as a group      |     |                       | 31,000 |     |               | 8,778,707 |     |                | 28.10 |

| Vote Required; Recommendation of the Board |

The affirmative vote of a simple majority of the votes cast in person or by proxy at the Annual Meeting is required for approval of this proposal. Abstentions

and broker non-votes will not have any effect on the outcome of voting on any of this proposal.

| THE BOARD OF DIRECTORS UNANIMOUSLY RECOMMENDS THAT SHAREHOLDERS VOTEFORAPPROVAL OF THE AMENDMENT TO THE COMPANY’S 2018 LONG TERM INCENTIVE PLAN TO INCREASE THE NUMBER OF ORDINARY SHARES AVAILABLE FOR ISSUANCE UNDER THAT PLAN BY 2,000,000 ORDINARY SHARES. |

| 2025 PROXY STATEMENT |     | 31 |

#### TABLE OF CONTENTS

### SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT
The following table presents information as to the beneficial ownership of our ordinary shares as of March 3, 2025, (except as noted) for:

• each person, or group of affiliated persons, known by us to beneficially own more than 5% of our ordinary shares;

• each of our directors;

• each of our executive officers named in the Summary Compensation Table - Fiscal Year 2024 below; and

• all of our directors and executive officers as a group.

Unless otherwise indicated, the address of each beneficial owner named below is c/o Prothena Corporation plc, 77 Sir John Rogerson’s Quay, Block C, Grand Canal Docklands, Dublin 2, D02 VK60, Ireland.

| Name of Beneficial Owner                         |     | Amount and Nature of Beneficial Ownership(1) |            |     |                   |     |   |     |              |     |            |     |             |     |       |
| 5% Shareholders:                                 |     | Shares                                       |            |     | Shares            
 Acquirable        
 Within 60 Days(2) |     |   |     | Total Shares 
 Deemed       
 Beneficially 
 Owned        |     |            |     | Percent of  
 Outstanding 
 Shares(3)   |     |       |
| Entities Associated with EcoR1