Boris Johnson will resign on Thursday after being told by senior Cabinet ministers that he no longer had their support.
Johnson has spoken to Tory 1922 Committee chairman Sir Graham Brady and agreed to stand down, with a new Tory leader set to be in place by the party conference in October.
A No.10 spokesperson said: “The prime minister will make a statement to the country today.”
The dramatic development came after over 50 Tory MPs quit their government posts.
A succession of backbenchers, including many who had supported him in last month’s vote of confidence, also made it clear that they now wanted him out.
That followed the shock resignations of Rishi Sunak and Sajid Javid on Tuesday night.
The PM managed to see off the immediate threat to his premiership by carrying out a hasty reshuffle, including sacking Michael Gove for disloyalty.
But the resignations continued on Wednesday morning, including Northern Ireland secretary Brandon Lewis, which quickly made it clear that Johnson was living on borrowed time.
During a disastrous appearance in front of the Commons liaison committee, cabinet ministers began arriving in No.10 so they could tell Johnson his time was up when he came back.
Astonishingly, a rival group of Johnson-supporting ministers, including Nadine Dorries, also arrived to give him their backing.
The PM had earlier struck a defiant tone during his committee appearance, repeatedly insisting that he had no intention of quitting. He said: “We’re going to get on with running the country.”