Tom Hayden, who burst out of the 1960s counterculture as a radical leader of America’s civil rights and antiwar movements, but rocked the boat more gently later in life with a progressive political agenda as an author and California state legislator, died on Sunday in Santa Monica, Calif. He was 76.

His wife, Barbara Williams, said he died in a hospital. He had been treated for heart problems and fell ill in July while attending the Democratic National Convention in Philadelphia. He lived in Los Angeles.

During the racial unrest and antiwar protests of the 1960s and early ’70s, Mr. Hayden was one of the nation’s most visible radicals. He was a founder of Students for a Democratic Society, a defendant in the Chicago Seven trial after riots at the 1968 Democratic National Convention, and a peace activist who married Jane Fonda, went to Hanoi and escorted American prisoners of war home from Vietnam.

As a civil rights worker, he was beaten in Mississippi and jailed in Georgia. In his cell he began writing what became the Port Huron Statement, the political manifesto of S.D.S. and the New Left that envisioned an alliance of college students in a peaceful crusade to overcome what it called repressive government, corporate greed and racism. Its aim was to create a multiracial, egalitarian society.