Rennie Davis, who lived out one of the more quixotic journeys of the 1960s generation when he went from leading opponent of the Vietnam War, as a convicted member of the Chicago Seven, to spokesman for a teenage Indian guru, died on Tuesday at his home in Berthoud, Colo. He was 80.

His wife, Kirsten Liegmann, who announced the death on his Facebook page, said the cause was lymphoma, adding that a large tumor had been discovered only two weeks ago.

Smart, charismatic and a blur of energy and engagement, Mr. Davis was a leading figure of the antiwar movement. After graduating from Oberlin College in Ohio, he joined the top ranks of the activist organization Students for a Democratic Society and the National Mobilization Committee to End the War in Vietnam.

In 1967, he and Tom Hayden, another S.D.S. leader, attended an international conference of student radicals in Bratislava, Czechoslovakia; traveled to Hanoi, the capital of North Vietnam; and returned in time for the march on the Pentagon immortalized in Norman Mailer’s 1968 book “The Armies of the Night.”

That experience led to Chicago, where Mr. Davis helped organize a motley assemblage of antiwar activists, political radicals and the theatrical revolutionaries known as Yippies with the aim of descending on the 1968 Democratic National Convention.

A rally at Grant Park on Tuesday, Aug. 27, turned into a riot, with helmeted police clubbing thousands of demonstrators, including Mr. Davis, who was left bloodied, his head swathed in bandages.

A national commission later called the clash a police riot, but federal officials charged Mr. Davis and seven others with conspiracy and inciting to riot. They went from being called the Chicago Eight to the Chicago Seven after the case of one of them, the Black Panther leader Bobby Seale, was severed from the others. (In the end, Mr. Seale was never tried.)

The Chicago Seven trial became a seminal moment of the ’60s — part legal drama, part political theater. Its story was told last year in the Aaron Sorkin film “The Trial of the Chicago 7.”

In 1970, after a tumultuous four-and-a-half-month trial, all seven defendants were acquitted of conspiracy, but Mr. Davis and four others — Abbie Hoffman, Jerry Rubin, David Dellinger and Mr. Hayden — were convicted of inciting to riot and sentenced to five years in prison. The verdicts were overturned on appeal, as were various contempt citations.