David E. McReynolds, a pacifist, socialist and sometime political candidate whose activism spanned many decades, died on Friday in Manhattan. He was 88.

The War Resisters League, where Mr. McReynolds had been a staff member, confirmed his death. He was taken to Mount Sinai Beth Israel hospital after falling in his Manhattan apartment, a friend, Bruce Cronin, said.

Mr. McReynolds was best known for his demonstrations against the draft during the Vietnam War, his advocacy of pacifism and denuclearization, and his two bids for president in 1980 and 2000 as an openly gay man running on the Socialist Party USA ticket.

“He’ll be known for the lifetime of leadership and the pacifist movements that, to a large degree, he defined in the post-World War II, Cold War era,” said Professor Cronin, the chairman of the political science department at City College of New York. “But what I think helped to define him was that he was as much a humanist as he was an activist.” He had met Mr. McReynolds at a denuclearization rally in the 1980s.