In a speech outside 10 Downing Street, Starmer - in office since July 2024 - conceded he had lost the support of his Labour party MPs.
He said he had informed King Charles III of his decision to resign so that a new Labour leader, and therefore prime minister, could be elected.
"I will remain in post as prime minister until the contest is complete, and I will do everything I can to ensure an orderly handover of power," he said.
U.K. Prime Minister Keir Starmer speaks outside 10 Downing Street on June 22, 2026. Photo by AP
Starmer's authority has been waning since Labour endured a drubbing in local and regional elections in May.
