WASHINGTON — Representative John Katko of New York, a centrist Republican who broke with his party last year to vote to impeach former President Donald J. Trump, announced on Friday that he would not run for re-election.

Mr. Katko was one of 10 House Republicans to vote to impeach Mr. Trump and is the third member of that group to announce his retirement.

In a statement that fell almost exactly one year after that vote, Mr. Katko said he decided to call it quits in order to “enjoy my family and life in a fuller and more present way.” He added that the loss of both his own parents and his wife’s parents in the last three years “provided life-changing perspective for me.”

“My conscience, principles, and commitment to do what’s right have guided every decision I’ve made as a member of Congress, and they guide my decision today,” he said.

Mr. Katko, a former federal prosecutor, had grown increasingly marginalized by conservatives at home and among House Republicans on Capitol Hill, who have demanded total loyalty to Mr. Trump, played down the severity of the Jan. 6 Capitol riot and eschewed working with President Biden. Those who veer off that course have found themselves attracting primary challengers, being pushed to the party’s sidelines, or both.

Mr. Katko sins in the eyes of his own party included supporting the creation of an independent commission to investigate the Capitol riot and backing a $1 trillion bipartisan infrastructure plan championed by Mr. Biden. He had already drawn three primary challengers and, if he survived that, was facing the likelihood of a brutal general election campaign.

New York Democrats, who tried and failed for years to oust him from the Syracuse-based seat, are currently eying new congressional lines that could make the district virtually unwinnable for Republicans, even in a year that officials in both parties believe favors the G.O.P.

Democrats and Mr. Trump found rare common ground to cheer Mr. Katko’s decision.

“Great news, another one bites the dust,” Mr. Trump, who had offered to help those vying to unseat Mr. Katko in a primary, said in a statement.

Abel Iraola, a spokesman for House Democrats’ campaign arm, said the retirement highlighted how the Republican Party’s rightward drift has made it “toxic for so-called G.O.P. moderates.”

Mr. Katko had been among a shrinking group of lawmakers who appealed to voters outside of his own party. When Mr. Biden won his central New York district in 2020 by 9 points in 2020, Mr. Katko prevailed by 10.

But the same centrist credentials that allowed Mr. Katko to hang onto his seat made him a target in conservative circles. After Republican leaders tasked him to work with Democrats on a proposal to create an independent Jan. 6 commission, they then abandoned the effort in favor of shielding Mr. Trump and the party from further scrutiny, urging lawmakers to oppose the plan Mr. Katko had negotiated.

When Democrats formed their own select committee to investigate the riot anyway, Mr. Katko infuriated hard-right members by voting in October to hold Stephen K. Bannon in criminal contempt of Congress for stonewalling their inquiry.

And Mr. Katko was one of 13 House Republicans who voted in November for the infrastructure bill, leading some in his party to brand him and the other G.O.P. supporters of the legislation “traitors,” and to call for Mr. Katko to be stripped of his leadership role on the Homeland Security Committee. He had been in line to become the panel’s chairman if Republicans won control of the House.

The anger from his right flank followed Mr. Katko home. The Conservative Party, a minor party in New York that backs Republicans in most races, had denounced him last April and formally withdrew its support from his re-election bid after he voted for a Democratic bill extending protections for gay and transgender rights.

Bernard Ment, the party chairman in Onondaga County, home to Syracuse, said that position was the last straw. In an interview, he called Mr. Katko a “Democrat,” though he retained support from his local Republican Party organization.

“He’s been the one guy who’s tried to work on both sides of the aisle,” Mr. Ment said. “The problem is he’s managed to alienate a lot of conservative voters and tick off a lot of Republicans, and I don’t think he can make up the ground with Democratic voters.”

Democrats who control New York state government in Albany are widely expected to try to pad the district with new Democratic voters as they redraw the state’s congressional districts in the coming weeks, giving their party a stark advantage in November. Three Democrats — two of them veterans — have already entered the race.

With Mr. Katko and his crossover appeal out of the way, Democrats are likely to be less fearful of a Republican winning his district, giving them more wiggle room to further expand their majority as they redraw the map. New lines could yield as many as four new seats for Democrats in the House and deny Republicans five they currently hold. (New York is slated to lose one congressional seat this year after nationwide reapportionment.)

Mr. Katko, for his part, has maintained that he was focusing on supporting his party’s policy priorities, lashing against Mr. Biden’s immigration policies in particular, and working to bring home results for his district. In a statement last year, he made clear how dangerous he believed the former president’s conduct was in the run up to Jan. 6.

“To allow the president of the United States to incite this attack without consequence is a direct threat to the future of our democracy,” Mr. Katko said. “For that reason, I cannot sit by without taking action.”

Nicholas Fandos reported from New York.