Senator Edward J. Markey, a progressive Massachusetts Democrat who has served in Congress for a half-century, defeated a much younger rival in a primary race on Tuesday, according to The Associated Press.

The victory by Mr. Markey, who at 80 is the oldest senator in his state’s history, came at a moment when many Democratic voters are anxious for the party’s aging leaders to make way for a younger generation. Mr. Markey used a fiercely progressive message and the support of many younger left-wing leaders to ward off Representative Seth Moulton, 47, a moderate Democrat who had campaigned on a message of generational change.

Mr. Markey will be an overwhelming favorite to win the November general election in deep-blue Massachusetts, positioning him to serve in the Senate until he is at least 86. When he arrived in the House in 1976, Apple was still developing its first widely used computer, and Elvis Presley was still making music. Mr. Markey moved to the Senate in 2013.

During the campaign, Mr. Moulton, who is from the North Shore of Massachusetts and was not yet born when Mr. Markey arrived in Congress, seized on a moment in a debate in which Mr. Markey acknowledged he did not know if he used artificial intelligence in his work. Mr. Moulton said it showed Mr. Markey was out of touch and not up to the challenge of legislating in a changing world.

But Mr. Markey, a longtime Malden resident clad in Nike sneakers and speaking in a thick accent that erases Rs, emphasized his progressive credentials, much as he had he had six years earlier when he dispatched Joseph P. Kennedy III, a scion of the Kennedy family. (The Kennedys, political royalty in Massachusetts, had never lost a race in the state before Mr. Markey’s 2020 triumph.)

This year, Mr. Markey targeted Mr. Moulton over his position on transgender rights. The younger congressman had urged his party after the 2024 election to shift its stance on transgender girls’ participation in girls’ sports, saying he did not want his daughters “getting run over on a playing field by a male or formerly male athlete.”

Mr. Markey, in turn, campaigned as a strong supporter of trans rights, declaring that his opponent had thrown trans kids “under the bus.” Mr. Moulton said he was sorry if his comments had hurt anyone, but he stood by their substance.

Elected Democrats, aware that polls indicate that most Americans do not think trans athletes should not be allowed to play in girls’ sports, have almost universally shied away from the issue since 2024. But in a primary in a deeply Democratic state, Mr. Markey appeared to have found a winning argument, saying that “I believe you can be right, but too soon.”

In the general election, Mr. Markey will face John Deaton, a Republican lawyer who also ran for Senate in 2024, losing overwhelmingly to Senator Elizabeth Warren. Mr. Deaton was unopposed in his primary.

Massachusetts is consistently among the bluest states in federal elections; in 1972 it was the only state won by the Democratic presidential nominee, Gov. George McGovern of South Dakota. It was the first state to legalize gay marriage.

A progressive cavalry also rallied to Mr. Markey’s cause. Senators Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts joined him on the campaign trail. And he received endorsements from younger progressives such as Representative Ayanna Pressley of Massachusetts and Alexandria Ocasio-Cortez of New York, who is selective about wading into Democratic races.

Ms. Ocasio Cortez, 36, issued a statement hailing Mr. Markey as an “inspiration to many of us who are committed to building a better future for all.”

Mr. Moulton had hoped to tap into frustration with the party’s older leaders. After Joseph R. Biden Jr.’s doomed effort in 2024 to win re-election to the White House in his ninth decade, younger Democratic challengers have piled into primaries across the country. Some have won: Democratic House incumbents have fallen to decades-younger contenders in races in Colorado, New York, Michigan and Connecticut.

But in each of those races, the insurgents melded their calls for generational change with progressive platforms. Democratic strategists said Mr. Markey’s progressive positions appeared to offer him a firewall against the relatively centrist Mr. Moulton.

Mr. Markey recently passed John Quincy Adams on the list of oldest Congress members from Massachusetts in history. But he does not yet top the list. A century ago, Representative William S. Greene, a onetime Fall River mayor, served in the House until he was 83.