Boris Johnson has confirmed his resignation as British prime minister, stating he is sad to be giving up the job but "them's the breaks".
Staff members assembled in Downing Street during the statement in an effort to show support for Mr Johnson. His wife Carrie Symonds was also present with their nine-month-old, Romy.
Mr Johnson said it is “clearly now the will” of the parliamentary Conservative Party that there should be a new leader.
He said: “It is clearly now the will of the parliamentary Conservative Party that there should be a new leader of that party and therefore a new prime minister.
“And I’ve agreed with Sir Graham Brady, the chairman of our backbench MPs, that the process of choosing that new leader should begin now and the timetable will be announced next week.
Mr Johnson said he had tried to persuade his Cabinet it would be “eccentric” to change prime minister now but “I regret not to have been successful in those arguments and of course it’s painful not to be able to see through so many ideas and projects myself.
“But as we’ve seen, at Westminster the herd instinct is powerful, when the herd moves, it moves."
He acknowledged that “in politics, no one is remotely indispensable”.
Mr Johnson said he sought to stay prime minister because he felt it was his “obligation” to continue to do what the Tories promised in 2019.
“I want to say to the millions of people who voted for us in 2019, many of them voting Conservative for the first time, thank you for that incredible mandate, the biggest Conservative majority since 1987, the biggest share of the vote since 1979.
Mr Johnson said he was immensely proud of the government's achievements.
"From getting Brexit done to settling our relations with the continent for over half a century, reclaiming the power for this country to make its own laws in Parliament, getting us all through the pandemic, delivering the fastest vaccine rollout in Europe, the fastest exit from lockdown, and, in the last few months, leading the West in standing up to Putin’s aggression in Ukraine.”
He pledged to support the next leader as he said some people would be “relieved” to see him go and expressed his sadness at leaving “the best job in the world”.
Mr Johnson thanked his wife, family and the civil service in his speech.
Boris Johnson said: “I want to thank Carrie and our children, and all the members of our family who have had to put up with so much for so long.”
He also thanked the “peerless British civil service” and the “fantastic NHS” who “helped to extend my own period in office”.
During the speech, heckles and booing from the nearby public were heard and at times seemed to fluster Mr Johnson.
It is believed that Mr Johnson will outline is plan which is to remain British prime minister until a successor is in place, expected to be by the time of the Conservative Party conference in October.
Speaking before Mr Johnson's speech, Labour leader Keir Starmer said Mr Johnson must not be allowed to “cling on” in No 10 once he has resigned as Tory leader and threatened to use a Commons confidence motion to oust him.
Mr Starmer said the resignation should have happened a long time ago.
"And all those who have been complicit should be utterly ashamed.
“The Tory party have inflicted chaos upon the country during the worst cost-of-living crisis in decades. And they cannot now pretend they are the ones to sort it out.
“They have been in power for 12 years. The damage they have done is profound," Mr Starmer said.
Mr Johnson began a reshuffle of his Cabinet shortly before he was set to announce his resignation and as calls grew for him to bow out now rather than remain in a caretaker role.
Shailesh Vara was appointed as Secretary of State for Northern Ireland replacing Brandon Lewis who stepped down on Thursday morning.
Kit Malthouse as Chancellor for the Duchy of Lancaster, the most senior minister in the Cabinet Office after the prime minister.
Since Tuesday night, more than 50 MPs have resigned from government or party roles when the mass exodus was triggered by the resignations of Rishi Sunak and Sajid Javid from the Cabinet.
Mr Johnson had sought to defy his critics and carry on in office, despite warnings from Cabinet colleagues that this was not sustainable.
But Mr Johnson’s refusal to accept that he had lost the trust of Conservative MPs triggered another wave of ministerial resignations this morning.
Around a third of all MPs who held non-Cabinet ministerial positions at the start of the week have now resigned.
Nadhim Zahawi, who was appointed Chancellor on Tuesday evening, told Mr Johnson to “do the right thing and go now”.
In a tweet accompanying a letter, Mr Zahawi said: “Prime Minister: this is not sustainable and it will only get worse: for you, for the Conservative Party and most importantly of all the country. You must do the right thing and go now.”
A source close to Nadhim Zahawi told the PA news agency: “The country needs a Chancellor and he will serve as long as he’s asked to do so.”
Northern Ireland Secretary Brandon Lewis was among those who resigned from the Cabinet early Thursday morning.
Mr Lewis told Mr Johnson the government requires “honesty, integrity and mutual respect” and it is “now past the point of no return”.
Mr Johnson rejected calls to quit on Wednesday and dramatically sacked Cabinet rival Michael Gove.
He met ministers in No 10 on Wednesday, where he was told he has lost the confidence of the Conservative Party and should not continue in office – but refused to listen.
Mr Gove is thought to have told Mr Johnson on Wednesday morning that it is time for him to quit.
That was followed by a delegation of Cabinet ministers going to Downing Street to tell Mr Johnson he should stand down after losing the trust of his MPs.