LONDON — Bowing to intense pressure from his own party, Prime Minister Boris Johnson of Britain said Thursday that he would step down, ending a stormy three-year tenure that was marked by a landslide election victory and a successful drive to pull Britain out of the European Union, but collapsed under the weight of relentless scandals.
Mr. Johnson insisted even on Wednesday night that he would fight to remain in power. But only hours later, he gave way, overwhelmed by a mutiny in his cabinet, a wave of government resignations and a devastating loss of party support — all prompted by his handling of the latest scandal to engulf his leadership.
“It is clearly now the will of the parliamentary Conservative Party that there should be a new leader,” Mr. Johnson said in a brief midday appearance outside 10 Downing Street. “The process of choosing that new leader should begin now.”
The decision capped a dizzying 48 hours in British politics that began on Tuesday evening with the unexpected resignations of two of the highest-ranking cabinet ministers, followed by dozens of resignations of other ministers and officials all day Wednesday and into Thursday morning.
Whoever takes over as prime minister will inherit a daunting set of challenges, with double-digit inflation, mushrooming labor unrest and the specter of a recession. Britain shares those problems with other advanced economies, but there is evidence that Brexit has imposed an extra burden on its economy.
And even with Mr. Johnson’s announcement, the fight over his status may not be finished. He said he would remain in his post until a new party leader was in place, a process that could take several months.
But some Conservatives argued that Mr. Johnson should not be allowed to stay, even as a caretaker figure. John Major, a former prime minister, wrote to one of the party’s top officials, Graham Brady, urging that Mr. Johnson either hand over his duties to the deputy prime minister, Dominic Raab, or that the party arrange for a swift election of a new leader by lawmakers, curtailing the decision-making role of rank-and-file party members.
Mr. Johnson made it clear he was leaving against his wishes, saying he had tried to hold on because “I felt it was my job, my duty, my obligation” to continue the work he had done since 2019, when he led the Conservative Party to a landslide election victory on a vow to “Get Brexit Done.”
His announcement contained no acknowledgment of his own role in his downfall, casting it instead as a reflection of his fellow lawmakers’ attitudes.
“I’ve tried to persuade my colleagues that it would be eccentric to change governments when we are delivering so much, when we have such a vast mandate, and when we are actually only a handful of points behind in the polls,” Mr. Johnson said to an audience that included his wife, Carrie, who held the couple’s baby daughter, Romy.
“But, as we’ve seen at Westminster, the herd instinct is powerful and when the herd moves, it moves,” Mr. Johnson added.
Mr. Johnson said he expected the timetable for his departure and the selection of a successor to be decided on Monday by the 1922 Committee, the powerful body that represents Conservative Party backbench lawmakers. At the very latest, the committee will want to install a new party leader, who will become prime minister, by the time of the annual party conference in the fall, which Conservatives hope to use as a chance to reset.
Among potential candidates are the two former Cabinet ministers whose bombshell resignations on Tuesday touched off the cascade of departures: Rishi Sunak, who was chancellor of the Exchequer, and Sajid Javid, who was the health secretary. Others include Liz Truss, the foreign secretary; Suella Braverman, the attorney general; and Nadhim Zahawi, who briefly replaced Mr. Sunak as chancellor. There are also two outsiders: Jeremy Hunt, a former foreign secretary who challenged Mr. Johnson for the party leadership in 2019; and Tom Tugendhat, the chairman of the Foreign Affairs Committee.
Mr. Johnson’s downfall scrambles the broader political landscape in Britain, where the opposition Labour Party had seized a small but persistent lead in the polls over the Conservatives ahead of the next election, which must take place no later than January 2025. While Labour politicians viewed the turmoil in the Tory party with relish, they may feel ambivalence about the departure of Mr. Johnson, a polarizing figure who has lost much of the vote-getting appeal he had in 2019.
Keir Starmer, the Labour leader, said it was “good news for the country that Boris Johnson has resigned,” but added: “It should have happened long ago.”
Mr. Johnson, the prime minister since July 2019, leaves a complicated legacy, marked by his aggressive defense of Ukraine but also by domestic programs that often seemed driven as much by political as policy considerations. The prime minister’s staunch support of Ukraine’s president, Volodymyr Zelensky, has made him a popular figure in Ukraine, and reinforced Britain’s role as a key member of the NATO alliance.
“I look forward to continuing our close cooperation with the government of the United Kingdom,” President Biden said Thursday, adding, “That includes maintaining a strong and united approach to supporting the people of Ukraine as they defend themselves against Putin’s brutal war on their democracy.”
At home, Mr. Johnson’s signature program, “leveling up,’’ which was aimed at elevating the economic prospects of Britain’s north, was marked by a notable absence of financing or a workable plan to execute it.
His hard-line stance toward migrants arriving at Britain’s shores pleased his conservative loyalists but drew condemnation from liberals and rights groups — most especially his recent plan to send refugees from Britain to Rwanda.
But it was yet another scandal that sealed Mr. Johnson’s fate. His latest troubles erupted last week after a Conservative lawmaker, Chris Pincher, became drunk at an exclusive London club, where, it was alleged, he groped two men. Despite earlier complaints of inappropriate behavior by Mr. Pincher, Mr. Johnson had appointed him in February to a senior party position.
Mr. Johnson at first denied being aware of the previous complaints, but it later emerged that he had known about them, and on Tuesday he apologized and acknowledged that it was a mistake to have named Mr. Pincher to the elevated position.
The Fall of Boris Johnson, Explained
Turmoil at Downing Street. Britain’s prime minister Boris Johnson said he would step down less than three years after his landslide election victory, following a series of scandals that have ensnared his government. Here’s what led to this:
For many Conservatives, it was a scandal too far — especially as Downing Street had sent out others, including a cabinet minister, to repeat erroneous statements on its behalf.
With his support in the party evaporating, Mr. Johnson claimed that the party’s victory in 2019 gave him a popular mandate. But constitutional experts dismissed that as a willful misreading of the British system.
“Britain has a parliamentary not a presidential system,” said Vernon Bogdanor, a professor of government at King’s College London. “Johnson’s authority came as leader of the Conservative Party in the House of Commons. But when the followers — Conservative M.P.’s — cease to follow, the leader ceases to lead.”
Despite everything stacked against him, Mr. Johnson did not go quietly. When one of his closest allies, Michael Gove, told him on Wednesday that it was time to go, he responded by firing Mr. Gove from his cabinet post that evening.
Still, the blows kept coming. Simon Hart, the Welsh secretary, was next to quit. The attorney general, Ms. Braverman, not only called for Mr. Johnson to go but also declared herself a candidate to succeed him.
By the end of Wednesday, so many ministers or senior aides had resigned that it threatened to cripple decision-making in several government departments. Downing Street said Mr. Johnson was at his desk on Thursday morning, working on how to reshuffle his top team.
But there were too many vacant jobs and too few loyalists to fill them.
Early on Thursday, another cabinet minister, Brandon Lewis, the Northern Ireland secretary, quit, saying that things were “now past the point of no return” and adding, “I cannot sacrifice my personal integrity to defend things as they stand now.”
Six lower-ranking ministers followed suit, including the security minister, Damian Hinds, and a Treasury minister, Helen Whately.
Mr. Johnson seems finally to have gotten the message when even those he had just promoted turned on him. Less than 48 hours after becoming chancellor, Mr. Zahawi demanded that Mr. Johnson stand aside. Then the cabinet’s newest member, Michelle Donelan, who had been appointed to replace Mr. Zahawi in his previous role as education secretary, resigned from her new position.
Soon after, word came from Downing Street that Mr. Johnson had acknowledged what had been evident for some time — that his time in the building was coming to an end, and that he would speak to the nation later on Thursday.