He had jetted in from his Dominican Republic beach holiday to drum up support despite a chorus of Tories warning his comeback would destroy the party and the country.
But hours after backers tonight claimed he had the 100 MPs he needed to get on the ballot, Mr Johnson declared he would not be standing after all.
The arrogant MP boasted he had led the Tories into a “massive election victory” and was “uniquely placed to avert a general election now” by fulfilling the 2019 manifesto.
He added: “I have sadly come to the conclusion that this would simply not be the right thing to do. You can’t govern effectively unless you have a united party in parliament.”
The former premier abandoned his dream of returning to No10, confessing he would be too divisive.
It means Rishi Sunak will almost certainly become Britain’s next Prime Minister on Monday night or Tuesday – the UK’s first ethnic minority PM.
Almost half of the 357 Tory MPs had publicly declared for Mr Sunak – while only 60 or so revealed they were backing Boris Johnson and fewer than 30 for Penny Mordaunt.
Unless Ms Mordaunt enjoys a late surge, a flood of Johnson backers or has substantial support in secret, she could miss out on the 100-MP threshold to get on the ballot.
Mr Johnson’s campaign team had spent the day trying to convince MPs they already had the 100 nominations needed to get his name on the ballot.
They hoped that would encourage other MPs to offer support and get him over the line.
It means Rishi Sunak is in pole position to be ‘crowned’ Prime Minister as soon as Monday.
But key figures backed Mr Sunak including right-wingers Kemi Badenoch and Suella Braverman, and MOD minister James Heappey.
A fresh poll of the wider public by Opinium found 45% prefer Rishi Sunak to be the PM, compared to just 27% for Boris Johnson.
And the former Chancellor’s total kept ticking up to around 150 while only a trickle of new Johnson backers, including Foreign Secretary James Cleverly, topped up his tally.
At 9pm Mr Johnson insisted he had just scraped over the threshold – but his support was dwarfed by the backing for Mr Sunak.
In an echo of his 2016 humbling – when he ditched his bid for leadership after being out-manoeuvred by Michael Gove – he admitted defeat 35 hours after landing in Britain in a bid to recapture his old job.
Boris Johnson, pictured at Gatwick Airport, had jetted in from the Dominican Republic to mount a bid (
He had already been accused of lying about his number of backers after they refused to be identified. When his backers claimed they’d reached 100 at 5pm, a source on Penny Mordaunt ’s campaign scoffed: “People think it’s a bluff – he’s been losing supporters”.
Despite boasting he had enough supporters, he begged Ms Mordaunt to quit the race and back his bid hours before he pulled out.
But Ms Mordaunt refused – and suggested he should drop out and back her instead, it’s understood.
It’s thought she “called his bluff” over his claim to have 100 backers in secret, saying some of them were actually supporting her.
Mr Johnson also held lengthy talks with his former Chancellor Mr Sunak on Saturday night, but they broke up without a unity pact.
Critics had warned if he succeeded in reclaiming the keys to Downing Street, the party and the nation would be thrown into new chaos.
The Commons Privileges Committee is due to interrogate him by Christmas on whether he misled Parliament over lockdown-busting parties in No10, first revealed by the Mirror.
If he is found in contempt of Parliament he could be suspended from the Commons or even face a by-election in his Uxbridge seat, which Labour believe they can win.
Ex-supporter Steve Baker backed Rishi Sunak saying today: “Boris would be a guaranteed disaster … It’s a guaranteed nailed-on failure and we cannot allow it to happen.”
Lib Dem deputy leader Daisy Cooper branded the Tory leadership race “a total farce” as calls mounted for a general election.
She said: “This is a humiliating climbdown for Boris Johnson and all the Conservative MPs who wanted to put him back in Number 10 after he lied and broke the law.
“The public will rightly be furious that they’re set to endure a third Conservative PM in just as many months.”
Attempts to build momentum behind Mr Johnson’s latest tilt for the top had already descended into farce.
Some MPs who called for him to quit in the summer urged colleagues to support his fresh grab for the premiership, just three and a half months later.
Urging the then PM to quit in July, ex-Chancellor Nadhim Zahawi said: “This is not sustainable and it will only get worse.
“I am heartbroken that he hasn’t listened and is now undermining the incredible achievements of this government.”
Yet today Mr Zahawi claimed: “He was contrite & honest about his mistakes. He’d learned from those mistakes how he could run No10 & the country better.”
Boris Johnson’s statement in full
The former PM issued a statement tonight saying: “In the last few days I have been overwhelmed by the number of people who suggested that I should once again contest the Conservative Party leadership, both among the public and among friends and colleagues in Parliament.
“I have been attracted because I led our party into a massive election victory less than three years ago – and I believe I am therefore uniquely placed to avert a general election now.
“A general election would be a further disastrous distraction just when the government must focus on the economic pressures faced by families across the country.
“I believe I am well placed to deliver a Conservative victory in 2024 – and tonight I can confirm that I have cleared the very high hurdle of 102 nominations, including a proposer and a seconder, and I could put my nomination in tomorrow.
“There is a very good chance that I would be successful in the election with Conservative Party members – and that I could indeed be back in Downing Street on Friday.
“But in the course of the last days I have sadly come to the conclusion that this would simply not be the right thing to do. You can’t govern effectively unless you have a united party in parliament.
“And though I have reached out to both Rishi and Penny – because I hoped that we could come together in the national interest – we have sadly not been able to work out a way of doing this.
“Therefore I am afraid the best thing is that I do not allow my nomination to go forward and commit my support to whoever succeeds.
“I believe I have much to offer but I am afraid that this is simply not the right time.”