6-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 6-K

Report of Foreign Private Issuer Pursuant to Rule 13a-16 or 15d-16 under the Securities Exchange Act of 1934

For the month of December 2025

Commission File Number 001-37626

Mesoblast Limited

(Exact name of Registrant as specified in its charter)

Not Applicable

(Translation of Registrant’s name into English)

Australia (Jurisdiction of incorporation or organization)

Silviu Itescu

Chief Executive Officer and Executive Director

Level 38

55 Collins Street

Melbourne 3000

Australia

(Address of principal executive offices)

Indicate by check mark whether the registrant files or will file annual reports under cover Form 20-F or Form 40-F:

Form 20-F ☑ Form 40-F ☐

INFORMATION CONTAINED ON THIS REPORT ON FORM 6-K

On December 17, 2025, Mesoblast Limited filed with the Australian Securities Exchange a new issue announcement, notification of issue, conversion or payment up of unquoted equity securities (Appendix 3G) which is attached hereto as Exhibit 99.1, and is incorporated herein by reference.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly organized.

Dated: December 17, 2025

INDEX TO EXHIBITS

exhibit991

Appendix 3G - Notification of issue, conversion or payment up of unquoted equity securities Appendix 3G - Notification of issue, conversion or payment up of unquoted equity securities 1 / 6 Announcement Summary Entity name MESOBLAST LIMITED Date of this announcement Wednesday December 17, 2025 The +securities the subject of this notification are: Total number of +securities to be issued/transferred ASX +security code Security description Total number of +securities to be issued/transferred Issue date New class - code to be confirmed WARRANTS 3 5,000,000 17/12/2025 Refer to next page for full details of the announcement +Securities issued as part of a transaction or transactions previously announced to the market in an Appendix 3B that are not quoted, and are not intended to be quoted, on ASX Exhibit 99.1

Appendix 3G - Notification of issue, conversion or payment up of unquoted equity securities Appendix 3G - Notification of issue, conversion or payment up of unquoted equity securities 2 / 6 Part 1 - Entity and announcement details 1.1 Name of entity MESOBLAST LIMITED We (the entity named above) give notice of the issue, conversion or payment up of the following unquoted +securities. 1.2 Registered number type ABN Registration number 68109431870 1.3 ASX issuer code MSB 1.4 The announcement is 1.5 Date of this announcement 17/12/2025 New announcement

Appendix 3G - Notification of issue, conversion or payment up of unquoted equity securities Appendix 3G - Notification of issue, conversion or payment up of unquoted equity securities 3 / 6 Part 2 - Issue details 2.1 The +securities the subject of this notification are: Previous Appendix 3B details: Announcement Date and Time 04-Sep-2025 09:56 Announcement Title New - Proposed issue of securities - MSB Selected Appendix 3B to submit quotation request A placement or other type of issue 2.3a.2 Are there any further issues of +securities yet to take place to complete the transaction(s) referred to in the Appendix 3B? No +Securities issued as part of a transaction or transactions previously announced to the market in an Appendix 3B that are not quoted, and are not intended to be quoted, on ASX

Appendix 3G - Notification of issue, conversion or payment up of unquoted equity securities Appendix 3G - Notification of issue, conversion or payment up of unquoted equity securities 4 / 6 Part 3A - number and type of +securities the subject of this notification (existing class or new class) where issue has previously been notified to ASX in an Appendix 3B Placement Details ASX +security code and description new unquoted class of security Date the +securities the subject of this notification were issued 17/12/2025 Any other information the entity wishes to provide about the +securities the subject of this notification Issue details Number of +securities 5,000,000 Were the +securities issued for a cash consideration? Please describe the consideration being provided for the +securities Commitment fee for up to US$50 million convertible note facility, which the Company can use at its option following shareholder approval at the 2025 AGM, announced by the Company on 4 September 2025. No

Appendix 3G - Notification of issue, conversion or payment up of unquoted equity securities Appendix 3G - Notification of issue, conversion or payment up of unquoted equity securities 5 / 6 Part 3C - number and type of +securities the subject of this notification (new class) ASX +security code New class - code to be confirmed +Security description WARRANTS 3 +Security type Options ISIN code   Date the +securities the subject of this notification were issued 17/12/2025 Will all the +securities issued in this class rank equally in all respects from their issue date? Have you received confirmation from ASX that the terms of the +securities are appropriate and equitable under listing rule 6.1? Please provide a URL link for a document lodged with ASX setting out the material terms of the +securities being issued. https://cdn-api.markitdigital.com/apiman-gateway/ASX/asx-research/1.0/file/2924-03038201-3A684030&v=undefined Options Details +Security currency AUD - Australian Dollar Exercise price AUD 2.50000000 Expiry date 17/12/2029 Details of the existing class of +security that will be issued upon exercise or conversion of this new class of company option MSB : ORDINARY FULLY PAID Any other information the entity wishes to provide about the +securities the subject of this notification Each warrant will convert into one ordinary share. The warrants can also be converted to American Depositary Receipts (ADRs), in which case 10 warrants will convert into 1 ADR at an exercise price of US$16.25 per ADR. Please note, 3 million warrants will only vest and become exercisable by the holders if the Company exercises its option under the convertible note facility. Issue details Number of +securities 5,000,000 No Yes

Appendix 3G - Notification of issue, conversion or payment up of unquoted equity securities Appendix 3G - Notification of issue, conversion or payment up of unquoted equity securities 6 / 6 Part 4 - +Securities on issue Following the issue, conversion or payment up of the +securities the subject of this notification, the +securities of the entity will comprise: The figures in parts 4.1 and 4.2 below are automatically generated and may not reflect the entity's current issued capital if other Appendix 2A, Appendix 3G or Appendix 3H forms are currently with ASX for processing. 4.1 Quoted +securities (Total number of each +class of +securities issued and quoted on ASX) ASX +security code and description Total number of +securities on issue MSB : ORDINARY FULLY PAID 1,282,967,187 4.2 Unquoted +securities (Total number of each +class of +securities issued but not quoted on ASX) ASX +security code and description Total number of +securities on issue MSBAI : OPTION EXPIRING VARIOUS DATES EX VARIOUS PRICES 88,119,029 MSBAA : WARRANTS 2 2,000,000 MSBAO : WARRANTS 15,027,327 MSBAP : ADS WARRANTS 884,838 New class - code to be confirmed : WARRANTS 3 5,000,000