Conceding that he had lost the support of the party membership, British Prime Minister Keir Starmer announced Monday he will resign once his Labour Party chooses a new leader.

"Throughout, and in the face of exceptional challenges, Keir has acted with principle, determination, and collaboration," Carney wrote on the platform X. "The world is safer and allies are more united because of his efforts."

Carney noted Starmer's work to support Ukraine by convening the Coalition of the Willing, a group of nations which has offered to safeguard a future ceasefire.

Carney also praised Starmer's work to "strengthen NATO, improve Arctic co-operation, and deepen the historic partnership between Canada and the United Kingdom."

"I am grateful for your friendship," he added.

Carney and Starmer both came into office with high popularity on a centre-left platform that included some fiscally conservative measures. The two have had several bilateral meetings in both London and Ottawa over the 15 months since Carney became prime minister.

Starmer struggled with economic promises and faced criticism for appointing scandal-linked figures. His position was undermined by dismal poll numbers and substantial losses in May elections at the local level.

One of Starmer's possible successors is former Manchester mayor Andy Burnham, who easily won a seat in the House of Commons in a recent byelection.

Burnham has promised not to raise taxes but it is not clear how he would position the U.K. in numerous areas, including foreign policy.

Starmer's resignation came the day before Britain marks the 10th anniversary of its vote to leave the European Union -- a decision that continues to roil the country's economy and politics.

This report by The Canadian Press was first published June 22, 2026.

-- With files from The Associated Press.