LONDON — Britain’s governing Conservatives will hold a no-confidence vote Monday that could oust Prime Minister Johnson from power, after months of growing discontent with a divisive politician whose career has survived multiple ups and downs.

If Mr. Johnson loses the vote among the 359 Conservative lawmakers, the party will choose a new leader, who will also become prime minister. If he wins, he can’t face another challenge for a year under current party rules.

While Mr. Johnson has weathered many political storms, he has recently struggled to turn the page on months of ethics scandals, most notably over rule-breaking parties in government buildings during COVID-19 lockdowns.

Disclosures that the prime minister and his staff repeatedly flouted restrictions they imposed on Britain in 2020 and 2021 have fueled outrage in the country at the scandal known as “partygate.”

Conservative Party official Graham Brady announced Monday that he had received enough letters from lawmakers demanding a vote on Johnson’s leadership to trigger one. That happens if 54 Tory legislators — 15 percent of the party’s group in the House of Commons — write to Mr. Brady.

“The threshold of 15 percent has been passed,” Brady said. He said the vote would take place in person in the House of Commons on Monday evening, with the result announced soon after.

Mr. Johnson’s Downing Street office said the prime minister welcomed the vote.

“Tonight is a chance to end months of speculation and allow the government to draw a line and move on, delivering on the people’s priorities,” it said.

Late last month an investigator’s report on “partygate” slammed a culture of rule-breaking inside the prime minister’s Downing Street office.

Civil service investigator Sue Gray described alcohol-fueled bashes held by Downing Street staff members at a time when pandemic restrictions prevented U.K. residents from socializing or even visiting dying relatives.

Ms. Gray said the “senior leadership team” must bear responsibility for “failures of leadership and judgment.”

The prime minister said he was “humbled” and took “full responsibility” — but insisted he would not resign. He urged Britons to “move on” and focus on Britain’s battered economy and the war in Ukraine.

But a growing number of Conservatives feel that Mr. Johnson, the charismatic leader who won them a huge parliamentary majority in 2019, is now a liability.

If Mr. Johnson is ousted it would spark a Conservative leadership contest, in which several prominent government ministers are likely to run.

Conservative lawmaker Roger Gale, a Johnson critic, said “we have some very good alternatives to the prime minister so we’re not short of choice.”

“Any single one of those people in my view would make a better prime minister than the one that we’ve got at the moment,” he told the BBC.

Discontent seems to have come to a head over a parliamentary break that coincided with celebrations of Queen Elizabeth II’s Platinum Jubilee. For many, the four-day long weekend was a chance to relax — but there was no respite for Mr. Johnson, who was booed by some onlookers as he arrived for a service in the queen’s honor at St. Paul’s Cathedral on Friday.

Cabinet minister Steve Barclay, a Johnson ally, said toppling the leader now would be “indefensible.”

“The problems we face aren’t easy to solve,” he wrote on the Conservative Home website. “Democracies around the world are all currently facing similar challenges. But under Boris Johnson’s leadership, our plan for jobs shows how we are navigating through these global challenges.

“To disrupt that progress now would be inexcusable to many who lent their vote to us for the first time at the last general election, and who want to see our Prime Minister deliver the changes promised for their communities.”