In 1970, when he was 36, Mr. Tunney ran for the Senate. He was blessed with a weak Republican opponent, the one-term incumbent George Murphy, a former actor and song-and-dance man whose age — he was in his late 60s — and health were issues. Mr. Murphy was also hurt by the revelation that while a senator he had been paid $20,000 a year as a public relations consultant for a movie company.
Mr. Tunney’s victory margin in 1970 was bigger than that of Ronald Reagan, who was re-elected California governor that year. Soon, Mr. Tunney was being mentioned as a possible running mate of Senator Edmund S. Muskie of Maine, who seemed to have the inside track for the Democratic nomination to run against President Richard M. Nixon in 1972. But Mr. Muskie’s campaign flamed out early in 1972.
That summer, Robert Redford starred in “The Candidate,” a film based on Mr. Tunney’s 1970 campaign, and the senator still appeared to have a bright future.
In 1974, the independent California Poll showed him to be more popular than Mr. Reagan, then in his last year as governor. In 1975, Mr. Tunney led a successful fight in the Senate to cut off funds for covert military operations by pro-American rebels in Angola. Mr. Tunney and like-minded lawmakers feared that involvement in Angola could lead to a Vietnam-like quagmire in Africa.
But many liberal Democrats were disenchanted with him. They thought he had been too slow to turn against the Vietnam War, which he had supported early on, and they were disappointed by his refusal to embrace a boycott of California grapes by striking farm workers.
Liberals found a champion in Tom Hayden, the former campus radical, who challenged Mr. Tunney in the 1976 Senate Democratic primary. Mr. Hayden raised a lot of money and was a surprisingly effective campaigner, accusing Mr. Tunney of being beholden to big business, though Mr. Tunney had supported antitrust legislation as a senator.
Mr. Hayden also sought to turn Mr. Tunney’s friendship with Senator Edward M. Kennedy against him, calling Mr. Tunney “a Chappaquiddick waiting to happen,” a reference to the 1969 incident in which the political aide Mary Jo Kopechne died when the car in which she was riding, driven by Mr. Kennedy, plunged off a bridge connecting the island of Chappaquiddick to Martha’s Vineyard in Massachusetts.
Mr. Hayden later apologized for the remark. But after finishing a strong second in the June primary, Mr. Hayden offered only the most tepid support for Mr. Tunney in the general election. And the Kennedy allusion, fair or not, fanned complaints that Mr. Tunney preferred the companionship of elite Easterners over the company of Californians.
In fact, Mr. Tunney was a transplanted Californian, having had a privileged childhood in the East. His father, the former heavyweight boxing champion Gene Tunney, read widely and aspired to social status to go with his ring riches. He achieved it in 1928, when he married Polly Lauder, an heiress to the Carnegie steel fortune.
John Varick Tunney was born on June 26, 1934, in New York City. He grew up in Connecticut with his brothers, Jay and Gene, who is deceased, and a sister, Joan, who is also deceased. He studied anthropology at Yale, graduating in 1956. He attended the Hague Academy of International Law, worked on John F. Kennedy’s 1958 Senate campaign in Massachusetts and roomed with Edward Kennedy at the University of Virginia Law School, graduating in 1959.
John Tunney later admitted to a certain immaturity and lack of purpose until, around the time he was in law school, he said, “I suddenly became aware of the fact that this world was cold and cruel, and that people were indeed very, very hungry.”
He practiced law briefly in New York City, then joined the Air Force as a judge advocate and was stationed near Riverside, Calif. He remained in California after leaving the service.
Six feet three inches tall and fit in his prime, John Tunney was often described as handsome (although his bulging eyes and prominent teeth had saddled him with the nickname “Horse” in prep school). He was a far more imposing physical presence than his 1976 opponent, Dr. Hayakawa, who stood about 5-foot-5 and often sported a tam-o’-shanter.
But Dr. Hayakawa, a world-renowned semanticist, had a priceless moment in the spotlight from his past. In 1968, when he was president of San Francisco State College, he climbed onto a sound truck used by student protesters and yanked out the wires to the microphones. Long afterward, the image resonated with Californians fed up with campus unrest.
On Nov. 2, 1976, Dr. Hayakawa received about 3.7 million votes to just under 3.5 million for Mr. Tunney, even though Democrats far outnumbered Republicans in California. Dr. Hayakawa was aided by a strong showing by President Gerald R. Ford, who carried California in his loss to Jimmy Carter. The numbers also suggested that some former supporters of Tom Hayden had voted for Dr. Hayakawa just to spite Mr. Tunney. (Dr. Hayakawa retired after one term.)
“When you get into public life, you’ve got to be prepared to take your knocks,” Mr. Tunney said after his defeat.
After leaving office, he practiced law, served on corporate boards and was active in civic and cultural affairs. He enjoyed skiing, fly-fishing, biking, hiking and travel with his wife, the former Kathinka Osborne, who had been an Olympic skier from Sweden.
In addition to his brother Jay, he is survived by his wife; their daughter, Tara; his sons, Mark and Edward; a daughter, Arianne, from his first marriage, to Mieke Sprengers, which ended in divorce; a stepson, Cedric Osborne; a stepdaughter, Dariane Hunt; and three grandchildren.
Mr. Tunney seemed content to view politics from afar after 1976, although he did appear at a 1980 Los Angeles fund-raiser for his old friend Edward Kennedy in Mr. Kennedy’s unsuccessful presidential bid that year. In 2003, Mr. Tunney joined two former Senate Democrats, George S. McGovern and Fred Harris, in opposing the war in Iraq.
In recent years, Mr. Tunney had homes in Sun Valley, Idaho; New York City; and Los Angeles.
In a 2013 interview with The Los Angeles Times, Mr. Tunney said he had good memories about his days in Washington, and he lamented the later “hostile” atmosphere he saw there. “It’s appalling what’s happening in Congress,” he said, “that these men and women who are elected to get things done are not even able to get to the point of an up-or-down vote.”
An earlier version of this obituary, using incorrect information from the family, misstated the location of John V. Tunney’s death. He died in the Brentwood neighborhood of Los Angeles, not in Santa Monica, Calif.