Company: WEBNF
Filing Date: 2025-06-26
Form Type: 424B5
Source: 0001104659-25-062718
Chunk: 2

Company: WESTPAC BANKING CORP
Filing Date: 2025-06-26
Form: 424B5
Chunk 2
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100.000% | ​ | ​ | ​ | US$750,000,000            | ​ | ​ | ​                     | ​ | 100.000% | ​ | ​ | ​ | US$750,000,000               | ​ |
| Underwriting Discounts(2)             | ​ | ​ | ​                  | ​ | 0.250%   | ​ | ​ | ​ | US$1,875,000              | ​ | ​ | ​                     | ​ | 0.250%   | ​ | ​ | ​ | US$1,875,000                 | ​ |
| Proceeds to Westpac (before expenses) | ​ | ​ | ​                  | ​ | 99.750%  | ​ | ​ | ​ | US$748,125,000            | ​ | ​ | ​                     | ​ | 99.750%  | ​ | ​ | ​ | US$748,125,000               | ​ |

(1) Plus accrued interest from July 1, 2025 if settlement occurs after that date. (2) The underwriters have agreed to reimburse us for certain of our expenses relating to this offering. See “Underwriting (Conflicts of Interest)” on page S-27for further information. The notes will not be listed on any securities exchange. Currently, there is no public market for the notes. The underwriters expect that the notes will be ready for delivery in book-entry form only through The Depository Trust Company and its participants, including Euroclear Bank SA/NV and Clearstream Banking S.A., on or about July 1, 2025. Joint Book-Running Managers

| ​ | BofA Securities | ​ | ​ | Citigroup | ​ | ​ | J.P. Morgan | ​ | ​ | Morgan Stanley | ​ | ​ | Westpac Banking Corporation | ​ |

Co-Managers

| ​ | CIBC Capital Markets | ​ | ​ | Rabo Securities | ​ | ​ | Scotiabank | ​ |

June 24, 2025

TABLE OF CONTENTS

TABLE OF CONTENTS PROSPECTUS SUPPLEMENT

| ​                                                 | ​ | ​ | Page |   |      |   | ​ |
| IMPORTANT NOTICES                                 | ​ | ​ | ​    | ​ | S-ii | ​ | ​ |
| PRESENTATION OF INFORMATION                       | ​ | ​ | ​    | ​ | S-iv | ​ | ​ |
| FORWARD-LOOKING STATEMENTS