Representative Mike Johnson of Louisiana won election on Wednesday as the 56th speaker of the House of Representatives, putting an end to three weeks of chaos that left the chamber without a leader and put Republican divisions on display.

Republicans elevated Mr. Johnson, 51, a little-known and deeply conservative lawmaker, after a tumultuous fight. It began after the hard right ousted Speaker Kevin McCarthy, and raged on as the divided House G.O.P. nominated and then quickly discarded three other candidates to succeed him.

Worn down by a brutal stretch of infighting that unleashed a barrage of recriminations and violent threats against lawmakers, both the hard-right flank of the party and mainstream Republicans united to elect Mr. Johnson in a 220-to-209 vote.

Republicans jumped to their feet and applauded after Representative Patrick T. McHenry of North Carolina, the interim speaker, declared that Mr. Johnson was the “duly elected speaker of the House of Representatives.”

A socially conservative lawyer who opposes abortion rights and same-sex marriage, Mr. Johnson also played a leading role in congressional efforts to overturn the 2020 election.

The vote on Wednesday put him in second in line to the presidency, capping an extraordinary period of twists and turns on Capitol Hill. The far right that has become a dominant force in the Republican Party rose up and effectively dictated the removal of an establishment speaker and the installation of an arch-conservative replacement.

In a speech that traced his ascent up the political ladder in Louisiana to Congress, Mr. Johnson pledged to try to “restore the people’s faith in this House.” He cited sending aid to Israel, fixing a “broken” southern border, and reining in federal spending as his top legislative priorities.

“The challenge before us is great, but the time for action is now,” Mr. Johnson said shortly after he was elected. “And I will not let you down.”

Evoking his evangelical Christian faith, Mr. Johnson repeatedly referenced scripture. “The Bible is very clear that God is the one that raises up those in authority,” he said. “He raised up each of you, all of us. And I believe that God has ordained and allowed each one of us to be brought here for this specific time.”

In a nod to the simmering frustrations among the hard-right flank of the party that ultimately deposed Mr. McCarthy, the California Republican, Mr. Johnson pledged that his office “is going to be known for decentralizing power.”

Elected to Congress in 2016, Mr. Johnson is the most junior lawmaker in decades to become speaker.

He may also be the most conservative. Mr. Johnson is the former chairman of the Republican Study Committee and sponsored legislation to effectively bar the discussion of sexual orientation or gender identity at any institution serving children younger than 10 that receives federal funds.

He served on former President Donald J. Trump’s impeachment defense team, played a leading role in recruiting House Republicans to sign a legal brief supporting a lawsuit seeking to overturn the 2020 election results and was an architect of Mr. Trump’s bid to object to certifying them in Congress on Jan. 6, 2021.

Democrats were scathing in their assessment of Mr. Johnson’s ascent to the speakership. Representative Pete Aguilar of California, the Democratic conference chairman, said that the speaker fight had devolved into a contest over “who can appease Donald Trump.” At that line, a handful of hard-right Republicans stood and applauded.

They heckled mainstream Republicans facing tough re-election contests next year in swing districts as they rose to vote for Mr. Johnson. After Representatives Mike Lawler and Marc Molinaro, both of New York, each voted for the Louisiana Republican, a Democrat could be heard yelling out: “Bye-bye!”

Mr. Johnson immediately faces a host of challenges that dogged his predecessor, Mr. McCarthy. He is confronting a mid-November deadline to pass a measure to fund the government to avert a shutdown. And he will need to lead a conference deeply divided over foreign policy as Congress considers the Biden administration’s $105 billion funding request for Israel, Ukraine and the southern border.

Mr. Johnson has opposed continued funding for the war in Ukraine, which has emerged as a bitter fault line in the G.O.P. and in the spending battles that he will have to navigate in the coming days.

After President Biden was told during a White House news conference that a new speaker had been elected, Mr. Biden said: “I hope that’s true. Because we have to get moving.”

Asked whether he was concerned, given the Republican speaker’s history, that he would try again to overturn the election in 2024, Mr. Biden answered flatly: “No. Just like I was not worried the last campaign would overturn the election.”

Mr. Johnson was able to bring together both the party’s hard-right and mainstream flanks that had taken turns sinking speaker candidates. But it was also clear that Republicans were eager to put an end to the weekslong spectacle of mass dysfunction and paralysis that many said had left their constituents distraught.

“From an outside point of view these last few weeks probably look like total chaos, confusion, no end in sight,” said Representative Tom Emmer of Minnesota, the No. 3 Republican who within hours of being nominated for speaker was dumped by his party’s hard-right flank. “But from my perspective, this is one of the greatest experiences in the recent history of our republic.”

Mainstream conservatives who backed Mr. Johnson said they were eager to pull the House out of its paralysis.

“While there are issues where we differ, we must get back to governing for the good of the country,” Mr. Lawler wrote on social media, posting a photo of himself and Mr. Johnson shaking hands.

A bloc of Republicans had objected to the speaker bid of Representative Jim Jordan of Ohio, the hard-right co-founder of the Freedom Caucus, because of his role in helping lead Mr. Trump’s efforts to overturn the election. But some said they did not have the same concerns about Mr. Johnson.

Representative Ken Buck of Colorado said that Mr. Johnson was not involved in postelection efforts to invalidate the results, even though Mr. Johnson was a critical player in those activities. “People can make mistakes and still be really good speakers,” Mr. Buck said.

And the hard-right Republicans who voted to oust Mr. McCarthy, setting into motion the three-week stretch of chaos that left the House without a leader, said Mr. Johnson’s ascension to the top job made their decision to depose the California Republican worth it.

“This affirms the path that we took,” Representative Bob Good of Virginia said.

Reporting was contributed by Luke Broadwater, Robert Jimison, Kayla Guo, Michael D. Shear and Erica L. Green.