Company: PRTA
Filing Date: 2025-03-28
Form Type: DEF 14A
Source: 0001559053-25-000017
Chunk: 0

Company: PROTHENA CORP PUBLIC LTD CO
Filing Date: 2025-03-28
Form: DEF 14A
Chunk 0
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#### TAB LE OF CONTENTS

### UNITED STATES

### SECURITIES AND EXCHANGE COMMISSION

#### Washington, D.C. 20549
#### ____________________

#### SCHEDULE 14A

#### Proxy Statement Pursuant to Section 14(a) of the

#### Securities Exchange Act of 1934
#### ____________________

| Filed by the Registrant |     | ☒ |     | Filed by a Party other than the Registrant |     | ☐ |

Check the appropriate box:

| ☐ |     | Preliminary Proxy Statement |

| ☐ |     | Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) |

| ☒ |     | Definitive Proxy Statement |

| ☐ |     | Definitive Additional Materials |

| ☐ |     | Soliciting Material Pursuant to § 240.14a-12 |

#### ____________________

### PROTHENA CORPORATION PUBLIC LIMITED COMPANY
<div align='center'>(Name of registrant as specified in its charter)</div>

#### ____________________

<div align='center'>(Name of Person(s) Filing Proxy Statement, if other than the Registrant)</div>

Payment of Filing Fee (Check all boxes that apply):

| ☒ |     | No fee required.                                                                                    |
| ☐ |     | Fee paid previously with preliminary materials.                                                     |
| ☐ |     | Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11 |

#### TAB LE 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 ANNUAL GENERAL MEETING OF

#### SHAREHOLDERS TO BE HELD ON MAY 13, 2025
To the Shareholders of Prothena Corporation plc:

NOTICE IS HEREBY GIVEN that the Annual General Meeting of Shareholders (the “Annual Meeting”) of Prothena Corporation plc, an Irish public limited company (the “Company”), will be held on Tuesday, May 13, 2025, at 4:00 p.m. local time, at The Merrion Hotel, Upper Merrion Street, Dublin 2, D02 KF79, Ireland for the following purposes:

1. To elect