Republican Kevin McCarthy has been elected speaker of the House of Representatives at the 15th attempt, overcoming resistance from his own ranks and tensions that boiled over on the floor of the chamber after a chaotic week that tested the party’s ability to govern.

“My father always told me, it’s not how you start, it’s how you finish,” he told cheering fellow Republicans.

Eager to confront President Joe Biden and the Democrats, he promised subpoenas and investigations, saying: “Now the hard work begins.”

The California Republican credited former president Donald Trump for standing with him and for making late calls “helping get those final votes”.

Republicans roared in celebration when his victory was announced, chanting “USA! USA!”

Mr McCarthy finally took the oath of office and the House was finally able to swear in newly elected legislators who had been waiting all week for the chamber to formally open and the 2023-24 session to begin.

After four days of ballots, Mr McCarthy convinced more than a dozen conservative holdouts to become supporters, including the chairman of the chamber’s Freedom Caucus.

After he had fallen one vote short in the 14th ballot, the chamber became raucous, and Mr McCarthy strode to the back of the chamber to confront Republican Matt Gaetz, sitting with Lauren Boebert and other holdouts. Fingers were pointed, words exchanged and violence apparently just averted.

At one point, Republican Mike Rogers, shouting, approached Mr Gaetz before another party colleague, Richard Hudson, physically pulled him back.

“Stay civil!” someone shouted.

Order restored, the Republicans fell in line to give Mr McCarthy the post he had fought so hard to gain, second in the line of succession to the presidency.

It was the end of a bitter standoff that had shown the strengths and fragility of American democracy.

The tally was 216-212 with Democrats voting for leader Hakeem Jeffries.

The resolution came after Mr McCarthy agreed to many of the detractors’ demands — including the reinstatement of a long-standing House rule that would allow any single member to call a vote to oust him from office.

Even as he secured the votes he needs, he will emerge as a weakened speaker, having given away some powers and constantly under the threat of being booted out by his detractors.

But he could also be emboldened as a survivor of one of the more brutal fights for the gavel in US history. Not since the Civil War era has a speaker’s vote dragged through so many rounds of voting.

The showdown that has stymied the new Congress came against the backdrop of the second anniversary of the January 6 attack on the Capitol, which shook the country when a mob of Trump supporters tried to stop Congress from certifying the Republican’s 2020 election defeat to Mr Biden.

At a Capitol event on Friday, some legislators, all but one of them Democrats, observed a moment of silence and praised officers who helped protect Congress on that day, and at the White House, Mr Biden handed out medals to officers and others who fought the attackers.

“America is a land of laws, not chaos,” he said.

One significant former holdout — Scott Perry, chairman of the conservative Freedom Caucus, who had been a leader of Mr Trump’s efforts to challenge the 2020 election — tweeted after his switched vote for Mr McCarthy: “We’re at a turning point.”

Another Republican holdout, Byron Donalds, who was repeatedly nominated as an alternative candidate for speaker, also switched on Friday to vote for Mr McCarthy.

Mr Trump may have played a role in swaying some holdouts — calling into a meeting of Republican freshmen the night before, and calling other members ahead of voting. He had urged Republicans to wrap up their public dispute.