Coburn was born in Laurel, Nebraska on August 31, 1928, the son of James Harrison Coburn II (1902–1975) and Mylet S. Coburn (née Johnson; 1900–1984). His father was of Scotch-Irish ancestry and his mother was an immigrant from Sweden. The elder Coburn had a garage business that was destroyed by the Great Depression. Coburn himself was raised in Compton, California, where he attended Compton Junior College.

In 1950, he enlisted in the United States Army, in which he served as a truck driver and occasionally a disc jockey on an Army radio station in Texas. Coburn also narrated Army training films in Mainz, Germany.

Coburn also appeared in dozens of television roles including, with Roberts, several episodes of NBC’s Bonanza. Coburn appeared twice each on two other NBC westerns Tales of Wells Fargo with Dale Robertson, one episode in the role of Butch Cassidy, and The Restless Gun with John Payne in “The Pawn” and “The Way Back”, the latter segment alongside Bonanza’s Dan Blocker. Butch Cassidy aired in 1958.

Coburn’s film debut came in 1959 as the sidekick of Pernell Roberts in the Randolph Scott western Ride Lonesome. He soon got a job in another Western Face of a Fugitive (1959).

Coburn was married twice. His first marriage was to Beverly Kelly, in 1959; they had two children together. The couple divorced in 1979 after twenty years of marriage.

During the 1960 to 1961 season, Coburn co-starred with Ralph Taeger and Joi Lansing in the NBC adventure/drama series, Klondike, set in the Alaskan gold rush town of Skagway.

Coburn also made two guest appearances on CBS’s Perry Mason, both times as the murder victim; in “The Case of the Envious Editor” and “The Case of the Angry Astronaut,” respectively. In 1962, he portrayed the role of Col. Briscoe in the episode “Hostage Child” on CBS’s Rawhide.

Coburn’s interest in fast cars began with his father’s garage business and continued throughout his life, as he exported rare cars to Japan. Coburn was credited with having introduced Steve McQueen to Ferraris, and in the early 1960s owned a Ferrari 250 GT Lusso and a Ferrari 250 GT Spyder California SWB. His Spyder was the thirteenth of just fifty-six built. Coburn imported the pre-owned car in 1964, shortly after completing The Great Escape.

Back at Fox, Coburn made a second Flint film, In Like Flint (1967), which was popular but Coburn did not wish to make any more. He went over to Paramount to make a Western comedy, Waterhole No. 3 (1967), and the political satire The President’s Analyst (1967). Neither film performed particularly well at the box office but over the years The President’s Analyst has become a cult film. In 1967 Coburn was voted the twelfth biggest star in Hollywood.

In July 1970 Richard F Zanuck of Fox dropped the $300,000 option it had with Coburn.

In 1971, Coburn starred in the Zapata Western Duck, You Sucker!, with Rod Steiger and directed by Sergio Leone, as an Irish explosives expert and revolutionary who has fled to Mexico during the time of the Mexican Revolution in the early 20th century. In 1964 Coburn said he would do A Fistful of Dollars if they paid him $25,000, which was too expensive for the production’s tiny budget. Duck You Sucker, also called A Fistful of Dynamite, was not as highly regarded as Leone’s four previous Westerns but was hugely popular in Europe, especially France.

Coburn went back to Italy to make another Western, A Reason to Live, a Reason to Die (1973). He then re-teamed with director Sam Peckinpah for the 1973 film Pat Garrett and Billy the Kid, in which he played Pat Garrett. In 1973 Coburn was voted the 23rd most popular star in Hollywood.

In 1973, Coburn was among the featured celebrities dressed in prison gear on the cover of the album Band on the Run made by Paul McCartney and his band Wings. Coburn was one of the pallbearers at the funeral of Bruce Lee along with Steve McQueen, Bruce’s brother, Robert Lee, Peter Chin, Danny Inosanto, and Taky Kimura. Coburn gave a speech: “Farewell, Brother. It has been an honor to share this space in time with you. As a friend and a teacher, you have given to me, have brought my physical, spiritual and psychological selves together. Thank you. May peace be with you”

Coburn was a martial arts student and a friend of fellow actor Bruce Lee. Upon Lee’s early death, Coburn was one of his pallbearers at the funeral on July 25, 1973.

Coburn returned to television in 1978 to star in a three-part mini-series version of a Dashiell Hammett detective novel, The Dain Curse, tailoring his character to bear a physical resemblance to the author. During that same year as a spokesman for the Joseph Schlitz Brewing Company, he was paid $500,000 to promote its new product in television advertisements by saying only two words: “Schlitz. Light.” In Japan his masculine appearance was so appealing he became an icon for its leading cigarette brand. He also supported himself in later years by exporting rare automobiles to Japan. He was deeply interested in Zen and Tibetan Buddhism, and collected sacred Buddhist artwork. He narrated a film about the 16th Karmapa called “The Lion’s Roar”.

Coburn was in a 4 year relationship with British singer-songwriter Lynsey de Paul from the late 1970s. They co-wrote her songs “Losin’ the Blues For You” and “Melancholy Melon” that appeared on her 1979 Tigers and Fireflies album.

Coburn moved almost entirely into supporting roles such as those of the villains in both High Risk (1981) and Looker (1981). He hosted a TV series of the horror-anthology type, Darkroom, in 1981 and 1982.

Coburn played the lead in the action film Sky Riders (1976) then played Charlton Heston’s antagonist in The Last Hard Men (1976). He was one of the many stars in Midway (1976) then had the star role in Sam Peckinpah’s Cross of Iron (1977) playing a German soldier. This critically acclaimed war epic performed poorly in the United States but was a huge hit in Europe. Peckinpah and Coburn remained close friends until Peckinpah’s death in 1984.

He supported Walter Mondale’s campaign in the 1984 presidential election.

Cal Spyder #2377 was repainted several times during Coburn’s ownership; it has been black, silver, and possibly red. He kept the car at his Beverly Hills-area home, where it was often serviced by Max Balchowsky, who also worked on the suspension and frame modifications on the Mustang GTs used in the filming of McQueen’s Bullitt. Coburn sold the Spyder in 1987 after twenty-four years of ownership. The car was restored, had several owners, and was sold in 2008 for $10,894,400 to English broadcaster Chris Evans. At that time it set a new world record for the highest price ever paid for an automobile at auction.

He later married actress Paula Murad Coburn, on October 22, 1993 in Versailles, France; they remained married until Coburn’s death in 2002, both he and his wife Paula set up “The James and Paula Coburn (charitable) Foundation”.

Because of his severe rheumatoid arthritis, Coburn appeared in very few films during the 1980s, yet he continued working until his death in 2002. This disease had left Coburn’s body deformed and in pain. “You start to turn to stone,” he told ABC News in an April 1999 interview. “See, my hand is twisted now because tendons have shortened.” For 20 years, he tried a host of both conventional and unconventional treatments, but none of them worked. “There was so much pain that…every time I stood up, I would break into a sweat,” he recalled. Then, at the age of 68, Coburn tried something called MSM, methylsulfonylmethane, a sulfur compound available at most health food stores. The result, he said, was nothing short of miraculous. “You take this stuff and it starts right away,” said Coburn. “Everyone I’ve given it to has had a positive response.” Though the MSM did not cure Coburn’s arthritis, it did relieve his pain, allowing him to move more freely and resume his career.

Coburn died of a heart attack at the age of 74 on November 18, 2002 while listening to music at his Beverly Hills home. Less than two years later, Paula died of cancer on July 30, 2004, at age 48.