Richard Trumka, the president of the A.F.L.-C.I.O., the nation’s pre-eminent labor federation, for the last 12 years and an influential voice in Democratic politics, died on Thursday. He was 72.

The cause was a heart attack, according to an A.F.L.-C.I.O. official, who did not say where Mr. Trumka died.

Senator Charles Schumer of New York, the Democratic leader, announced the deathon the Senate floor. “The working people of America have lost a fierce warrior at a time when we needed him most,” Mr. Schumer said in an emotional tribute.

Mr. Trumka was elected to lead the federation in 2009, after serving as secretary-treasurer, its second-ranking official, since 1995, and president of the United Mine Workers of America before that.

Under the A.F.L.-C.I.O. constitution, the federation’s current secretary-treasurer, Liz Shuler, will take over as president until its executive council can meet to elect a successor. The federation’s next presidential election was originally scheduled to take place this year, but was delayed until next year because of the pandemic.

While the percentage of Americans represented by unions continued its long-term decline on his watch, to less than 11 percent, Mr. Trumka was close to the two Democratic presidents during his tenure, and had been an influential outside voice in helping to shape President Biden’s ambitious jobs and infrastructure proposals.

Mr. Trumka, a third-generation coal miner from Pennsylvania, went to work as a staff attorney for the United Mine Workers after getting his law degree. In 1982, at 33, he was elected on a reform ticket to head the mine workers’ union.

A full obituary will be published soon.

Emily Cochrane contributed reporting.