Boris Johnson won a confidence vote against him on Monday night after scraping through the vote with 211 Tory MPs supporting his leadership, while 148 votes were cast against him.
The under-fire PM won with just 59% of the vote despite a last-ditch attempt to win support from the backbenches with a speech to the 1922 Committee earlier on Monday.
Mr Johnson had retained strong support from his backbenchers throughout the Covid pandemic, but he has recently struggled to keep their backing after he was accused of breaking his own lockdown rules.
After civil servant Sue Gray published her report into lockdown parties in No. 10, which criticised a "failure of leadership", there had been a steady drip-drip of Tories announcing they have submitted no confidence letters.
The PM may have narrowly won the vote - but how have other Conservative Party leaders fared in no confidence votes?
Theresa May faced a vote of confidence in her leadership on December 12 2018.
The news was announced early that morning by Sir Graham Brady, who was the chairman of the backbench 1922 Committee of MPs at the time, as he is now.
A total of 317 Conservative MPs were able to vote, meaning Mrs May needed at least 159 to win a majority.
The result was announced at 9pm, with 200 MPs (63%) saying they had confidence in Mrs May and 117 (37%) saying they had no confidence: a majority of 83 - significantly more than Mr Johnson's majority of 63.
This was enough for Mrs May to continue in the short term as both party leader and prime minister.
But just five months later she announced her resignation, following repeated failures to get her Brexit deal through the House of Commons and a disastrous performance by the Conservatives in the European elections.
Iain Duncan Smith
Iain Duncan Smith had been leader of the Conservative Party for just over two years when he faced and lost a vote of confidence.
It was the first time a ballot of this kind had taken place within the party.
Given the comparatively low number of Conservative MPs in the House of Commons at the time, only 25 letters of no-confidence were needed to trigger the contest.
The threshold was reached on October 28 2003 and the vote took place the following day, with 75 MPs (45%) saying they had confidence in Mr Duncan Smith but 90 (55%) saying they had no confidence.
He announced he would step down as soon as his successor was chosen, which happened just over a week later when Michael Howard was elected leader unopposed.
Nearly five years after becoming Conservative leader, and three years after winning a general election, John Major triggered the equivalent of a vote of confidence in himself.
He announced his resignation as leader on June 22 1995, challenging his critics within the Tory party to back him or sack him and stressing that in the future he would expect total support from his parliamentary colleagues.
John Redwood resigned as secretary of state for Wales to stand against Mr Major and the election took place on July 4.
Mr Major needed a simple majority of the 329 Conservative MPs in the House of Commons to win the contest.
But although he secured 218 votes, 111 MPs – a third of the party – either voted for Mr Redwood, spoiled their ballot papers or abstained.
Mr Major continued as leader and prime minister until losing the 1997 general election, which took place on May 1 1997, almost two years after the 1995 leadership election.
Under previous rules in the Conservative Party, a leadership election could take place once a year.
In November 1989, Sir Anthony Meyer, the little-known MP for Clwyd North West, took advantage of this procedure to launch a challenge against Margaret Thatcher, who had been prime minister for a decade and Tory leader for 14 years.
He did not expect to win but instead used the election to test the level of opposition to Mrs Thatcher within the party.
The result was a large victory for Mrs Thatcher, who received the backing of 84% of MPs.
But the 16% who either voted for Sir Anthony, spoiled their ballot papers or abstained was a signal of unhappiness among backbenchers.
These feelings of disquiet grew over the following 12 months, culminating in another leadership challenge in November 1990, this time from Michael Heseltine.
The election took place on November 20 and saw Mrs Thatcher win 204 votes and Mr Heseltine 152.
This was not enough for Mrs Thatcher to pass the two thresholds specified in the party rules, which stated the winner needed more than 50% of the overall vote but also to be 15% clear of the runner-up.
She initially declared she would contest a second ballot, before withdrawing two days later after canvassing the opinion of close colleagues.
Douglas Hurd and John Major then decided to join the contest, and the second ballot – held on November 27 – was won by Mr Major with 185 votes, followed by Mr Heseltine on 131 and Mr Hurd on 56.
Both Mr Heseltine and Mr Hurd promptly withdrew from the contest, removing the need for a third ballot and meaning Mr Major became leader and prime minister unopposed.
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