Boris Johnson is quitting as Tory leader after ministers and MPs made clear his position was untenable.
He will remain as Prime Minister until a successor is in place, expected to be by the time of the Conservative Party conference in October.
A No 10 source said Mr Johnson spoke to Sir Graham Brady, chairman of the Conservative 1922 Committee, to inform him of his decision.
“The Prime Minister has spoken to Graham Brady and agreed to stand down in time for a new leader to be in place by the conference in October,” a No 10 source said.
Johnson will make a statement to the country later today confirming the decision.
The resignation comes after the Prime Minister haemorrhaged support among his ministers and MPs.
More than 50 MPs have resigned from government or party roles since Tuesday night, when the mass exodus was triggered by the resignations of Rishi Sunak and Sajid Javid from the Cabinet.
The Prime Minister had sought to defy his critics and carry on in office, despite warnings from Cabinet colleagues that this was not sustainable.
Earlier today, the new Education Secretary Michelle Donelan resigned, while the new Chancellor Nadhim Zahawi told Johnson: “You must do the right thing and go now.”
Other resignations included:
James Cartlidge quit as courts’ minister, telling Johnson: “The position is clearly untenable.”
Technology minister Chris Philp resigned, saying the “PM should step down given public and Parliamentary confidence has clearly gone, and given the importance of integrity in public life”.
Pensions minister Guy Opperman resigned, telling Johnson “recent events have shown clearly that the government simply cannot function with you in charge”.
Security minister Damian Hinds resigned, saying: “It shouldn’t take the resignation of dozens of colleagues, but for our country, and trust in our democracy, we must have a change of leadership.”
Treasury minister Helen Whately resigned, telling Johnson there “are only so many times you can apologise and move on”.
Northern Ireland Secretary Brandon Lewis resigned from the Cabinet, telling the Prime Minister that government requires “honesty, integrity and mutual respect”.
The pound was trading higher on the news of Johnson’s resignation – up 0.6% at 1.198 US dollars and 0.4% stronger at 1.174 euros.
SNP Westminster leader Ian Blackford MP said: "Boris Johnson's resignation is welcome but for Scotland it changes very little – we’re still controlled by a Westminster system that saw fit to make him Prime Minister.
"Whoever replaces him, Scotland will still be saddled with a Tory government we didn't vote for imposing Brexit, austerity cuts and damaging policies against Scotland's will.
"Whoever takes over from Boris Johnson must respect the democratic mandate Scotland has to hold an independence referendum so we can escape Westminster control for good."
Scottish Labour leader Anas Sarwar said: "The entire country will be breathing a sigh of relief that Boris Johnson is going, but let's not forget that whoever replaces him is complicit.
"This is a party that is rotten to the core, that allowed a cheat, a charlatan, a man devoid of any principles or any values to become the Prime Minister of this country – and they inflicted his carnage on this country for years.
"That's why not only do we need to see the back of Boris Johnson, we also need to see the back of this Tory government – and that's why we need an election to elect a Labour government that can bring the values of decency, integrity and principles back into our country."
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