Johnson's decision makes his rival Rishi Sunak almost certain to be the nation's next prime minister.
Former British Prime Minister Boris Johnson has said he will not run to lead the Conservative Party, ending intense speculation about a comeback.
While he believed he was well-placed to deliver another Conservative victory in the 2024 general election, he was standing aside in the interests of party unity, he said in a statement on Sunday.
"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.
Johnson, who was ousted in July amid ethics scandals, was widely expected to run to replace Liz Truss, who quit last week.
He has spent the weekend trying to gain support from fellow lawmakers, and said he had amassed more than 100 votes, the threshold to run.
But he was far behind former Treasury chief Rishi Sunak in support. Johnson said he had concluded that “you can’t govern effectively unless you have a united party in Parliament.”
Former British Treasury chief Rishi Sunak was the frontrunner on Sunday in the Conservative Party's race to replace Liz Truss as prime minister.
Sunak garnered the public support of over 100 Tory lawmakers to forge ahead of his two main rivals: former prime minister Boris Johnson and ex-Cabinet minister Penny Mordaunt.
But widespread uncertainty remained after British media reported that Sunak held late-night talks with Johnson on Saturday. Speculation mounted that the pair could strike a deal to unite the fractured governing party after it was left reeling from Truss' rapid downfall following Johnson's ouster.
READ MORE: Rishi Sunak leads in race to replace Truss, Johnson yet to declare
According to British media, former Prime Minister Boris Johnson has pulled out of the Conservative leadership race pic.twitter.com/XEXKtDsL2M— TRT World Now (@TRTWorldNow) October 23, 2022
Sunak is likely next leader
The Conservative Party hastily ordered a contest that aims to finalise nominations on Monday and install a new prime minister — its third this year — within a week.
Sunak, 42, was runner-up after Truss in this summer's Tory leadership race to replace Johnson after he was forced out by a string of ethics scandals.
Sunak has the backing of at least 124 Conservative lawmakers, according to unofficial tallies compiled by British news organisations. That's well ahead of the 100 nominations required to qualify.
“There will be integrity, professionalism and accountability at every level of the government I lead and I will work day in and day out to get the job done," Sunak said in a statement.
UK Business Secretary Jacob Rees-Mogg told the BBC on Sunday that he spoke with Johnson and “clearly he's going to stand" after flying back to London on Saturday from a vacation in the Dominican Republic.
The party has 172,000 members.
READ MORE: As Liz Truss resigns, what’s next for Britain?