Boris 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.
The PM will quit as Tory leader after ministers and MPs made clear his position was untenable, with support crumbing around him in recent days.
Downing Street appointed Greg Clark as the new Levelling Up Secretary, replacing Michael Gove who was sacked by Mr Johnson on Wednesday, while James Cleverly has been made Education Secretary.
Robert Buckland has been appointed Secretary of State for Wales, following the resignation of Simon Hart.
Kit Malthouse is the new Chancellor of the Duchy of Lancaster, the most senior minister in the Cabinet Office after the Prime Minister.
Shailesh Vara is the new Secretary of State for Northern Ireland, while Andrew Stephenson has been appointed Minister without Portfolio, and will attend Cabinet.
Mr Johnson will remain as Prime Minister until a successor is in place, expected to be by the time of the Conservative Party conference in October.
But critics of the PM have suggested he should not be allowed to stay in office until the autumn.
George Freeman, who quit as science minister on Thursday morning, said that now Mr Johnson had “finally done the decent thing” he should “hand in the seals of office, apologise to Her Majesty, allow her to appoint a caretaker under whom ministers can serve, so the Conservative Party can choose a new leader properly”.
Lord Barwell, who served as Theresa May’s chief of staff, said the leadership election must be “relatively quick” and there was a “question whether the PM will be able to lead a caretaker government in the meantime, will enough ministers agree to serve?”
Dominic Cummings, formerly Mr Johnson’s right-hand man in No 10 but now one of his most fierce critics, said the Prime Minister would cause “carnage” if he was allowed to remain in position and suggested Dominic Raab should stand in as a caretaker premier.
He suggested the Cabinet should give Mr Johnson an ultimatum and tell him that if he does not go the Queen will appoint Deputy Prime Minister Mr Raab and “cops escort you from building”.
Labour leader Sir 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.
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.
But resignations continued and Chancellor Nadhim Zahawi – who was only appointed to the role on Tuesday – went public with his call for the Prime Minister to quit.
The timetable for the Tory leadership contest will be agreed between the 1922 Committee, which runs the parliamentary proceedings to whittle the candidates down to two, and Conservative headquarters.
Leadership jostling had already begun before Mr Johnson signalled he would resign.
Attorney General Suella Braverman and arch-Brexiteer Steve Baker have both indicated they will run.
Business Secretary Kwasi Kwarteng also hinted that he will throw his hat in the ring.
“What a depressing state of affairs,” he said. “So much needless damage caused.
“We now need a new leader as soon as practicable. Someone who can rebuild trust, heal the country, and set out a new, sensible and consistent economic approach to help families.”
Foreign Secretary Liz Truss, who is widely expected to run, cut short an official trip to Indonesia and is expected to issue a statement.
