The PM 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 spokesman said: “The Prime Minister will make a statement to the country today.”
It came after an avalanche of resignations, with the number of cabinet members, ministers and other MPs quitting Government and party posts topping 50 by Tuesday night.
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Around a third of all MPs who held non-Cabinet ministerial positions at the start of the week had resigned by 9am on Thursday.
Chancellor Nadhim Zahawi, only appointed on Tuesday to replace Rishi Sunak, was among those resigning this morning, calling for Mr Johnson to “leave with dignity” and “go now” as the Prime Minister’s refusal to quit triggered another wave of ministerial resignations.
Mr Zahawi said he had made clear privately to Mr Johnson that he should go but “I am heartbroken that he hasn’t listened and that he is now undermining the incredible achievements of this Government at this late hour”.
Hexham MP Guy Opperman was also among those resigning this morning. He left his role as pensions minister, telling Mr Johnson that “recent events have shown clearly that the Government simply cannot function with you in charge”.
George Freeman, who announced he was resigning as science minister on Thursday morning, said Boris Johnson must apologise to the Queen and advise her to call for a caretaker prime minister.
He tweeted: “Boris Johnson needs to hand in the seals of office, apologise to Her Majesty and advise her to call for a caretaker prime minister.
“To take over today so that ministers can get back to work and we can choose a new Conservative leader to try and repair the damage and rebuild trust.”