AltaGas (ATGFF) 6-KMaterial Change Report

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 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 June 2022

Commission File Number: 333-235922

ALTAGAS LTD.

(Translation of Registrant’s Name into English)

1700, 355 – 4^th Avenue S.W., Calgary, Alberta, T2P 0J1, Canada

(Address of Principal Executive Offices)

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

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): ¨

Exhibit 99.1 to this report on Form 6-K is hereby incorporated by reference into the registrant’s Registration Statement on Form F-10 (333-253122). The remaining exhibit to this report on Form 6-K is furnished, not filed, and will not be incorporated by reference into any registration statement filed by the registrant under the Securities Act of 1933, as amended.

Exhibit Index

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.