Peace activist Tom Hayden, whose radical views were at the forefront of the anti-Vietnam War movement in the 1960s, has died. He was 76.

Hayden's wife, Canadian actress and author Barbara Williams, told CNN that he died late Sunday at the UCLA Medical Center in Santa Monica, California, from complications related to a 2015 stroke. He is also survived by the couple's son, Liam.

On Twitter, his official account hailed him as a "1960s radical who became a champion of liberal causes."

Hayden was a member of the "Chicago 7" convicted on federal charges of conspiracy and incitement to riot over anti-Vietnam War protests at the 1968 Democratic National Convention. The conviction was overturned on appeal.

As an ideological leader of the influential Students for a Democratic Society, he authored its Port Huron statement, a visionary document that still inspires anti-authoritarian and pro-democracy movements today.

"We are people of this generation, bred in at least modest comfort, housed now in universities, looking uncomfortably to the world we inherit," reads the document's first line.

He later served for almost two decades as a California state lawmaker, both in the State Assembly and the Senate, and was married to actress and fellow political activist Jane Fonda from 1973 to 1990. The couple had two children.

Liberal leaders quickly paid tribute to Hayden.

"A political giant and dear friend has passed. Tom Hayden fought harder for what he believed than just about anyone I have known. RIP, Tom," tweeted Los Angeles Mayor Eric Garcetti.

Alan Spencer, who was recruited by Hayden to write debate material in the 1980s, praised his former boss, saying "he shook up the system, made an impact."

Hayden taught at various universities, including the University of California, Los Angeles, Scripps College, Pitzer College, Occidental College and the Harvard Institute of Politics.

He was also a prolific author, editing and writing about 20 books. His last volume is due to be published in March.

"At time when we need revived peace movement, Tom Hayden's (forthcoming) book 'Hell No: The Forgotten Power of the Vietnam Peace Movement' will be vital," The Nation magazine editor and publisher Katrina vanden Heuvel wrote hours before news of Hayden's death broke.

Hayden was a columnist and member of the editorial board of the magazine.