LONDON -- Prime Minister Boris Johnson announced his resignation Thursday amid a mass revolt by top members of his government, marking an end to three tumultuous years in power in which he brazenly bent and sometimes broke the rules of British politics.

Months of defiance ended almost with a shrug as Johnson stood outside No. 10 Downing St. and conceded that his party wanted him gone.

"Them's the breaks," he said.

The brash, 58-year-old politician who took Britain out of the European Union and steered it through COVID-19 and the war in Ukraine was brought down by one scandal too many - this one involving his appointment of a politician who had been accused of sexual misconduct.

The messiest of prime ministers did not leave cleanly. Johnson stepped down immediately as Conservative Party leader but said he would remain as prime minister until the party chooses his successor. The timetable for that process will be announced next week. The last leadership contest took six weeks.

But many want him to go now, with some Conservative politicians expressing fear he could do mischief even as a caretaker prime minister.

鈥淚t's very difficult to see how Boris Johnson, given the character that he is, is going to be able to govern for three months in quiet humility and contrition,鈥� said George Freeman, who resigned as science minister on Thursday.

Among the possible candidates to succeed Johnson: former Health Secretary Sajid Javid, former Treasury chief Rishi Sunak, Foreign Secretary Liz Truss and Defense Secretary Ben Wallace.

About 50 Cabinet secretaries, ministers and lower-level officials quit the government over the past few days because of the latest scandal, often castigating the prime minister as lacking integrity.

The mass resignations stalled the business of some parliamentary committees because there were no ministers available to speak on the government's behalf.

Johnson clung to power for days, defiantly telling lawmakers on Wednesday that he had a 鈥渃olossal mandate鈥� from the voters and intended to get on with the business of governing.

But he was forced to concede defeat Thursday morning after one of his closest allies, newly appointed Treasury chief Nadhim Zahawi, publicly told him to resign for the good of the country.

鈥淚n the last few days, I tried to persuade my colleagues that it would be eccentric to change governments when we're delivering so much and when we have such a vast mandate,鈥� Johnson said. 鈥淚 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.鈥�

He said it is 鈥渃learly now the will of the parliamentary Conservative Party that there should be a new leader of that party and therefore a new prime minister.鈥�

Critics said the speech showed Johnson, to the end, refusing to take responsibility for or admit his mistakes.

Many Britons reacted to news of his resignation with relief and surprise, given his habit of digging in.

鈥淚t felt like he can just keep on going and keep on ignoring it, so I was bit surprised this morning when saw it on my phone,鈥� Himmat Dalyway, an investment trader in his 20s, said outside an Underground station in London. 鈥淎re you still 100% sure that he is going?â鈧�³

As Johnson gathered his cobbled-together Cabinet for a meeting after his resignation announcement, he promised not to rock the boat in his remaining weeks. He told members the government would not 鈥渟eek to implement new policies or make major changes of direction.鈥�

It was a humiliating defeat for Johnson, who not only pulled off Brexit but was also credited with rolling out one of the world's most successful mass vaccination campaigns to combat COVID-19.

But the perpetually rumpled, shaggy-haired leader known for answering his critics with bombast and bluster was also dogged by allegations he behaved as if the rules did not apply to him.

He managed to remain in power despite accusations that he was too close to party donors, that he protected supporters from bullying and corruption allegations, and that he misled Parliament about government office parties that broke COVID-19 lockdown rules.

When allegations of Downing Street parties emerged, Johnson told lawmakers 鈥渢here was no party鈥� and no rules were broken. But when photos of the prime minister raising a glass in front of a group of people surfaced, critics, some of them inside the Conservative Party, said Johnson had lied to Parliament - traditionally a resigning matter.

The prime minister was fined by police over the parties and survived a no-confidence vote last month in Parliament in which 41% of Conservative lawmakers tried to oust him.

Johnson became prime minister in July 2019, succeeding Theresa May, who resigned after Parliament rejected the Brexit agreement she negotiated with the EU. Johnson pushed his own Brexit deal through in an often messy and turbulent debate.

With his mop of unruly blond hair, he often looked like a schoolboy who had just rolled out of bed and run to class with his pajamas under his clothes.

In his rise to power he showed many of the same habits and abilities that would carry him far but also spell his downfall: He was an ebullient, attention-loving mayor of London; a journalist who was fired for making up a quote and filed exaggerated stories about EU excesses; and a politician with an Eton- and Oxford-honed talent for colorful oratory and the thrust and parry of debate.

He became known for his light regard for the truth and his glib and offensive remarks. He called Papua New Guineans cannibals and likened Muslim women who wear face-covering veils to 鈥渓etter boxes.鈥�

Recent disclosures that Johnson knew about sexual misconduct allegations against a Conservative lawmaker before he promoted him to a senior position in government proved to be one scandal too many.

The crisis began when Chris Pincher resigned as deputy chief whip amid accusations that he had groped two men at a private club. That triggered a series of reports about past allegations against Pincher.

Johnson offered shifting explanations about what he knew and when he knew it. That just heightened the sense that the prime minister couldn't be trusted.

Key Cabinet members Javid and Sunak, who were responsible, respectively, for fighting COVID-19 and inflation, resigned within minutes of each other Tuesday. That set off the wave of departures by their colleagues.

Now with a leadership election upon them, the Conservatives will have to decide whether they can stomach Johnson as a caretaker leader, a job that normally entails saying little and doing nothing.

鈥淭o be honest, I think a lot of the public will want to see him gone straightaway,鈥� said Tim Bale, a professor of politics at Queen Mary, University of London. 鈥淵ou know, they don't want to see him hanging around like a bad smell in Downing Street.鈥�