6-K

UNITED STATES

SECURITIES AND EXCHANGECOMMISSION

Washington, D.C. 20549

Form 6-K

REPORT OF FOREIGN PRIVATEISSUER

PURSUANT TO RULE 13a-16OR 15d-16

UNDER THE SECURITIESEXCHANGE ACT OF 1934

For the month of November 2022

Commission File Number 001-35866

KNOT Offshore PartnersLP

(Translation of registrant’s name intoEnglish)

2 Queen’s Cross,

Aberdeen, 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

On November 1, 2022, KNOT Offshore Partners LP (the “Partnership”) held its previously-adjourned 2022 annual meeting of limited partners (the “2022 Annual Meeting”) at 3:00 P.M. (UK time) at One Elmfield Park, Bromley, BR1 1LU, United Kingdom. At the 2022 Annual Meeting, resolutions were passed (i) to elect Edward A. Waryas, Jr. as a Class I Director of the Partnership whose term will expire at the 2026 annual meeting of limited partners and (ii) to ratify the appointment of Ernst & Young AS as the Partnership’s independent public accounting firm for the fiscal year ending December 31, 2022.

THIS REPORT ON FORM 6-K IS HEREBY INCORPORATED BY REFERENCE INTO THE FOLLOWING REGISTRATION STATEMENTS:

2

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.

3