John V. Tunney applauding a speech at the 1980 Democratic National Convention by his former law school roommate, Sen. Edward M. Kennedy (Mass.). (AP)

John V. Tunney, a U.S. congressman and senator from California once hailed for his Kennedy­esque manner and whose 1970 Senate campaign inspired the Oscar-winning film “The Candidate,” starring Robert Redford, died Jan. 12 in Los Angeles. He was 83.

The cause was prostate cancer, his brother, Jay Tunney, told the Associated Press.

Mr. Tunney was the son of Gene Tunney, a heavyweight boxing champion of the 1920s, and was a law school classmate and close friend of the late Sen. Edward M. Kennedy (D-Mass.).

Standing 6-foot-3, with a shock of blond hair, Mr. Tunney was a compelling figure on the campaign trail, first winning election to the U.S. House as a Democrat in 1964. After three terms representing a district south of Los Angeles, he ran for the Senate in 1970, defeating Republican incumbent George Murphy. At 36, Mr. Tunney was the youngest member of the Senate at the time and seemed to have a golden political future.

In 1972, one of his campaign workers, Michael Ritchie, directed “The Candidate,” a dark comedy about a Senate election in California, in which Redford played a long-shot candidate running against an aging incumbent. The film’s screenplay, by Jeremy Larner — a former campaign worker with 1968 presidential candidate Eugene J. McCarthy — won an Academy Award.

Then-congressional candidate John V. Tunney stands between his father, Gene Tunney, left, and Jack Dempsey, both retired boxing heavyweight champions, in 1964. (AP)

Redford’s character grows increasingly disillusioned by the internal pressures and machinations of the political world — a point of view that Mr. Tunney later came to share.

During his six years in the Senate, Mr. Tunney was unusually active for a first-term lawmaker, sponsoring more than three-dozen bills that were enacted into law. He helped lead efforts for antitrust reform and was a primary sponsor of the Noise Control Act of 1972. In 1975, he helped expand the Voting Rights Act.

Mr. Tunney was seen as a possible vice-presidential contender in 1972 and had a liberal voting record that included opposition to the Vietnam War and support for abortion rights and gun control. Yet when he ran for reelection in 1976, he was challenged from the left in the California Democratic primary by Tom Hayden, a onetime student activist and the husband of actress Jane Fonda.

Mr. Tunney prevailed, but in the general election he faced a political newcomer, S.I. Hayakawa, a 70-year-old former college president. Hayakawa won a narrow victory with support from conservative voters who applauded the way he stood up to campus demonstrators at San Francisco State University.

Mr. Tunney returned to California to practice law and never ran for elective office again.

“There is nothing sadder,” he said, “than a 42-year-old former senator hanging around Washington.”

John Varick Tunney was born June 26, 1934, in New York City and grew up on an estate near Stamford, Conn. His father defeated Jack Dempsey to claim the world heavyweight title in 1926 and won a controversial rematch a year later. He retired from boxing in 1928, went into business and married Polly Lauder, an heiress to the fortune of industrialist Andrew Carnegie.

The younger Mr. Tunney studied anthropology at Yale University, graduating in 1956. He then attended law school at the University of Virginia, where he met Kennedy on the first day of class. They were roommates in their second and third years and won a law-school moot-court competition together. Mr. Tunney received his law degree in 1959 and later served in the Air Force Judge Advocate General Corps.

Mr. Tunney, who grew up as a Republican, developed an interest in politics while working on Kennedy family campaigns and changed his party affiliation to Democrat. When he first ran for office in 1964, his father and Dempsey campaigned for him in precincts populated by Dust Bowl refugees of the 1930s.

“The Okies and Arkies, who had settled in [the] Coachella Valley and Imperial Valley, they didn’t like guys from Yale or Harvard, but they did like prizefighters,” Mr. Tunney said in a 2007 oral history interview with the Edward M. Kennedy Institute for the American Senate. “They loved Jack Dempsey and Gene Tunney.”

Mr. Tunney practiced law until 1987 and, in later years, took up other interests, ranging from poetry to the study of cosmology. He had homes in Los Angeles, New York and Sun Valley, Idaho.

His first marriage, to Mieke Sprengers, ended in divorce. Survivors include his wife of 40 years, the former Kathinka Osborne of Los Angeles; three children from his first marriage; a daughter from his second marriage; two stepchildren; a brother; and two grandchildren.

Mr. Tunney remained close to Kennedy, who died in 2009, and occasionally spoke out against what he considered the deteriorating quality of political discourse in recent decades.

He recalled, in the 2007 oral history interview, that he was one of seven senators to vote for a nationwide ban on handguns, except for the police and military. Mr. Tunney, who was close to both John F. Kennedy and Robert F. Kennedy before they were felled by assassins’ bullets, said he was proud of putting principle ahead of political expediency.

“I knew it was politically unpopular but I didn’t care,” Mr. Tunney said. “I said to myself, ‘I’m never going to vote for a bill that I think would allow again a guy like Bobby Kennedy to be assassinated.’ ”