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 September 2021

Commission File Number 001-35866

KNOT Offshore Partners LP

(Translation of registrant’s name into English)

2 Queen’s Cross,

Aberdeen, Aberdeenshire

AB15 4YB

United Kingdom

(Address of principal executive office)

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

Form 20-F   x             Form 40-F   ¨

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101 (b)(1).

Yes   ¨             No    x

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101 (b)(7).

Yes   ¨             No    x

EXHIBITS.

THIS REPORT ON FORM 6-K IS HEREBY INCORPORATED BY REFERENCE INTO THE REGISTRATION STATEMENT ON FORM F-3 (NO. 333-248518) OF THE REGISTRANT.

SIGNATURE

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 authorized.