Boris Johnson is to stand down as Conservative Party leader after losing the support of his ministers and MPs.
A Conservative leadership contest will take place this summer and a new prime minister will be in place in time for the party conference in October.
In the meantime, Mr. Johnson will continue as prime minister.
He had vowed to “keep going” following a wave of resignations from the government over his leadership but has now decided to step down.
But was urged to stand down by senior members of his cabinet, including newly-appointed chancellor Nadhim Zahawi.
In his resignation letter, Mr. Zahawi, who was given the job less than 48 hours ago, said he had “made clear to the prime minister” that he should “leave with dignity”.
Mr. Johnson is expected to give a resignation statement outside No 10 Downing Street later.