Hagman was born on September 21, 1931, in Fort Worth, Texas. His mother, Mary Martin, became a Broadway actress and musical comedy star after his birth. His father, Benjamin Jackson Hagman, who was of Swedish descent, was an accountant and lawyer who worked as a district attorney. Hagman’s parents divorced in 1936 when he was five years old. He lived with his maternal grandmother, Juanita Presley Martin, in Texas and California while his mother became a contract player with Paramount in 1938. In 1940, Hagman’s mother met and married Richard Halliday before giving birth to a daughter, Heller, the following year. Hagman attended a strict academy, Black-Foxe Military Institute and briefly Woodstock Country School, a boarding school in Vermont.

When his mother moved to New York City to resume her Broadway career, Hagman again lived with his grandmother in California. A few years later, his grandmother died and Hagman joined his mother in New York City. In 1946, Hagman moved back to his hometown of Weatherford and attended Weatherford High School, from which he graduated. One summer, he worked for oilfield-equipment maker Antelope Tool Company. Although his father wanted Hagman to become a lawyer and join his practice, he was drawn to drama classes and reportedly fell in love with the stage. He graduated from high school in 1949 and decided to pursue acting. He attended Bard College, New York, majoring in dance and drama but dropped out after one year.

Hagman began his career in 1950 acting in productions at Margaret Webster’s school at The Woodstock Playhouse in Woodstock, New York. That summer, during a break from his one year at Bard College, he worked in Dallas as a production assistant and acting in small roles in Margo Jones’s theater company. He appeared in The Taming of the Shrew in New York City, followed by numerous tent show musicals with St. John Terrell’s Music Circus in St. Petersburg, Florida, and Lambertville, New Jersey. In 1951, Hagman appeared in the London production of South Pacific with his mother, and stayed in the show for nearly a year. In 1952, Hagman received his draft notice and enlisted in the United States Air Force.

The release of a Columbia single performed with his mother Mary Martin, Get Out Those Old Records, in 1950, was credited to Mary Martin And Her Son Larry, with orchestra by Mitch Miller. It was released in Australia as a 78 rpm single, catalogue number DO-3409.

In 1954, Hagman married Swedish-born Maj Axelsson (born May 13, 1928, in Eskilstuna, Södermanlands län, Sweden – died May 31, 2016, in Los Angeles, California); they had two children, Heidi Kristina (born 1958) and Preston (born 1962). Longtime residents of Malibu, California, they then moved to Ojai. Hagman was a member of the Peace and Freedom Party from the 1960s. Hagman derided U.S. President George W. Bush prior to the Iraq War.

Stationed in London, he spent the majority of his military service entertaining U.S. troops in the United Kingdom and at bases in Europe. After leaving the Air Force in 1956, Hagman returned to New York City, where he appeared in the off-Broadway play Once Around the Block, by William Saroyan. That was followed by nearly a year in another off-Broadway play, James Lee’s Career. His Broadway debut occurred in 1958 in Comes a Day. Hagman appeared in four other Broadway plays, God and Kate Murphy, The Nervous Set, The Warm Peninsula, and The Beauty Part. During this period, he also appeared in numerous, mostly live, television programs.

Hagman’s first television role was as Kenneth Davidson in the 1957 episode “Saturday Lost” of the syndicated crime drama, Decoy, starring Beverly Garland as the first female police officer in a television lead. In 1958, he joined Barbara Bain as a guest star in the short-lived adventure-drama series Harbormaster, and appeared three times on Lloyd Bridges’ syndicated adventure series, Sea Hunt. In 1960, he was cast in the CBS summer medical series Diagnosis: Unknown in the role of Don Harding in the episode, “The Case of the Radiant Wine”. In 1961, Hagman joined the cast of daytime soap opera The Edge of Night as Ed Gibson, and stayed in that role for two years. In 1963 and 1964, he appeared twice in segments of the CBS legal drama, The Defenders

Hagman had a long friendship with actor Carroll O’Connor, beginning in 1959 when Hagman was starring in the Broadway play God and Kate Murphy and O’Connor was working as an assistant stage manager. Later, as the two struggled as young actors, they rented apartments near each other in New York. Over the years, they had a lot in common; just as O’Connor had renegotiated his contract for his salary on All in the Family in 1974, a consequence of missing two episodes, Hagman eventually found himself renegotiating his salary on Dallas, with similar results. Hagman’s daughter, Heidi, whom O’Connor had known since her childhood, joined the cast for one season of Archie Bunker’s Place. Hagman directed several episodes of O’Connor’s later series, In the Heat of the Night. They both endured serious health issues, with O’Connor’s heart bypass surgery, and Hagman’s liver transplant. Hagman remained close after O’Connor’s loss of his son Hugh, and through the rest of O’Connor’s life, delivering a eulogy at the funeral.

In 1964, he made his film debut in Ensign Pulver, which featured a young Jack Nicholson. That same year, he also appeared in Fail-Safe, with Henry Fonda.

In 1965, Hagman was cast as “genie” Barbara Eden’s master and eventual love interest, Air Force Captain (later Major) Anthony Nelson, in the NBC situation comedy I Dream of Jeannie, which ran for five seasons from 1965 to 1970. The show entered the top 30 in its first year and was NBC’s answer to the successful 1960s magical comedies, Bewitched on ABC and My Favorite Martian on CBS. Two reunion movies were later made, both televised on NBC: I Dream of Jeannie: 15 Years Later (1985) and I Still Dream of Jeannie (1991), but Hagman did not appear in either of them. At Dragon Con, in 2010, Hagman said he was never approached about it.

In 1969, Hagman’s friend, musician David Crosby, supplied him with LSD after a concert: “LSD was such a profound experience in my life that it changed my pattern of life and my way of thinking and I could not exclude it [from my autobiography].” Hagman was introduced to marijuana by Jack Nicholson as a safer alternative to Hagman’s heavy drinking. “I liked it because it was fun, it made me feel good, and I never had a hangover.” Although Hagman was a member of a 12-step program, he publicly advocated marijuana as a better alternative to alcohol.

He also directed (and appeared briefly in) a low-budget comedy and horror film in 1972 called Beware! The Blob, also called Son of Blob, a sequel to the classic 1958 horror film The Blob. This was the only feature film he directed.

In 1973, his stepfather Richard Halliday died, and Hagman reconciled with his mother, Mary Martin, soon after. The two were close until her death from colon cancer in 1990.

In 1978, Hagman was offered two roles on two television series that were debuting. One was for The Waverly Wonders and the other for Dallas, in the role of conniving elder son and businessman J.R. Ewing. When Hagman read the Dallas script at his wife’s suggestion, they both concluded it was perfect for him. Hagman based his portrayal in part on memories of the eldest son who had won the Antelope Tool Company succession battle.

Dallas became a worldwide success, airing in 90 countries – most notably the United Kingdom, where it saw its highest viewership outside the United States and was regularly enjoyed by members of the country’s Royal Family – and inspiring several primetime soaps. Hagman became one of the best-known television stars of the era. Producers were keen to capitalize on that love/hate family relationship of J.R., building anticipation to a fever-pitch in “A House Divided”, the 1980 cliffhanger season finale in which J.R. is shot by an unknown assailant, leading to the world-wide “Who shot J.R.?” phenomenon. The person who pulled the trigger was later revealed to be Kristin Shepard (played by Mary Crosby) in the “Who Done It?” episode which aired on November 21, 1980; Kristin was J.R.’s scheming sister-in-law and mistress, who shot him in a fit of anger.

At the beginning of the fourth season later that year, audience and actors were trying to guess “Who shot J.R.?”, now one of fictional TV’s most famous questions. During the media buildup, Hagman was involved in contract negotiations, delaying his return in the fourth season. Holding out for a higher salary, Hagman did not appear in the first episode of the show until the final few minutes. Producers were faced with a dilemma of whether to pay the greatly increased salary or to write J.R. out of the program. Lorimar Productions, the makers of the series, began shooting different scenes of Dallas which did not include Hagman. In the midst of negotiations, Hagman took his family to London for their July vacation. He continued to fight for his demands and network executives conceded that they wanted J.R. to remain on Dallas. From then on, Hagman became one of the highest-paid stars in television. At the beginning of the 1980–81 season, writers were told to keep the storylines away from the actors until they really found out who actually shot J.R., and it took three weeks until the culprit was revealed on November 21, 1980, in a ratings record-breaking episode.

For his performance as J.R. Ewing, Hagman was nominated for two Emmy Awards for Outstanding Lead Actor in a Drama Series in 1980 and 1981, but did not win. He was also nominated for four Golden Globe Awards, between 1981 and 1985. He was nominated for a Soap Opera Digest award seven times for Outstanding Villain on a Prime Time Serial, Outstanding Actor in a Leading Role on a Prime Time Serial, Favorite Super Couple: Prime Time and Outstanding Actor in a Comic Relief Role on a Prime Time Serial, and won five times. Hagman received the Golden Plate Award of the American Academy of Achievement from Academy member Ray Lee Hunt at the 1981 Achievement Summit in Dallas. In 1984, co-star Barbara Bel Geddes left Dallas, following a contract dispute that had resulted from her March 1983 quadruple heart bypass surgery. At one point, Hagman suggested to his real-life mother Mary Martin that she play Miss Ellie, but she rejected the suggestion and Bel Geddes was briefly replaced by Donna Reed for the 1984–1985 season, before Bel Geddes returned in better health for the 1985–1986 season. By the end of its 14th season in 1991, ratings had slipped to the extent that CBS decided to end Dallas. Hagman was the only actor to appear in all 357 episodes. He had also made five guest appearances on the Dallas spin-off series Knots Landing in the early 1980s. Some years after Dallas ended, Hagman appeared in two subsequent Dallas television movies: J.R. Returns in 1996, and War of the Ewings in 1998.

In 1980, Hagman recorded a single called “Ballad of the Good Luck Charm”.

Hagman starred in two short-lived series in the 1970s, The Good Life (1971-1972) and Here We Go Again (1973). In 1993, Hagman starred in Staying Afloat as a down-on-his-luck former millionaire who agrees to work undercover with the FBI to maintain his playboy lifestyle. Originally ordered for two TV movies and a weekly series by NBC, the pilot movie aired in November 1993 to critical drubbing and low ratings, ending production.

In 1995, Hagman underwent a life-saving liver transplant after he was diagnosed with liver cancer which was most likely brought on by approximately 40 years of heavy drinking. His clinical picture was further complicated by cirrhosis of the liver which had been diagnosed three years earlier in 1992. Hagman did not receive preferential treatment as a celebrity, with a 1995 UPI article stating that the donor liver “matched Hagman’s anonymous physical profile listed with the United Network for Organ Sharing.”

In January 1997, Hagman starred in a short-lived television series titled Orleans as Judge Luther Charbonnet, which lasted only eight episodes. In 2002, he made an appearance in the fourth series of Vic Reeves and Bob Mortimer’s British comedy panel game, Shooting Stars, often appearing bewildered at the nonsensical questions and the antics of the hosts – during the show Hagman even stated that he would fire his agent as a result. In January 2011, Hagman made a guest appearance in the seventh season of Desperate Housewives as a new husband for Lynette Scavo’s mother, Stella (played by Polly Bergen).

In 1999, after 29 years, Hagman agreed to reunite with Jeannie co-stars Barbara Eden and Bill Daily and creator/producer Sidney Sheldon on The Donny and Marie Show. In 2002, when I Dream of Jeannie was set to join the cable channel TV Land, Hagman once again took part in an I Dream of Jeannie reunion with Eden and Daily, this time on Larry King Live. On the TV Land Awards in March 2004, Hagman and Eden were the first presenters to reunite on stage. The following October, Hagman and Daily appeared at The Ray Courts Hollywood Autograph Show. And the following year, 2005, brought all three surviving stars from I Dream of Jeannie to the first cast reunion at the Chiller Expo Show.

In 2001, Hagman wrote his autobiography titled Hello Darlin’: Tall (and Absolutely True) Tales About My Life. In a 2007 interview, Hagman discussed his support for alternative energy. On a 2008 episode of Living With Ed, Hagman and his wife showed actor Ed Begley Jr. their solar powered, super energy efficient home named “Heaven” and talked about their green lifestyle. Maj Hagman was diagnosed with Alzheimer’s disease in 2008, and Hagman at first took the lead in caring for her, but her condition deteriorated. By 2010, she required 24-hour nursing care. As a result, Hagman put their 43-acre estate in Ojai up for sale listing it at $11 million.

Hagman and Eden reunited in March 2006 for a publicity tour in New York City to promote the first-season DVD of I Dream of Jeannie. He reunited once again with Eden on stage in the play Love Letters at the College of Staten Island in New York and the United States Military Academy, West Point, New York. The appearance marked the first time the two performers had acted together since Eden appeared with Hagman in a five-episode arc on Dallas in 1990.

In 2010, Hagman was hired as a spokesman for SolarWorld, a German solar energy commercial enterprise. While the SolarWorld commercials do not specifically mention either Dallas or J. R. Ewing, Hagman essentially revisits the character (complete with a picture of Hagman as J. R. Ewing from the original series on the mantle), stating that his oil company days are long over, “though still in the energy business”, meaning solar energy instead, which alternative energy now plays a major part of the next-generation Ewing family war between Christopher and John Ross III.

In June 2011, Hagman said he had stage 2 throat cancer. He commented, “As J. R. I could get away with anything — bribery, blackmail and adultery. But I got caught by cancer. I do want everyone to know that it is a very common and treatable form of cancer. I will be receiving treatment while working on the new Dallas series. I could not think of a better place to be than working on a show I love, with people I love.” Hagman had an acorn-sized tumor removed from his tongue in 2011. In June 2012, the cancer was said to be in remission. Then, in July 2012, doctors diagnosed Hagman with myelodysplastic syndromes (formerly known as preleukemia).

Hagman reprised his role as J.R. Ewing in TNT’s continuation of Dallas, which began in 2012. In 2011, while filming the new series, Hagman said, “Of course it’s fun to play the villain.” As a result of Hagman’s death in 2012, his character J.R. was killed off in season two of Dallas. Unused footage of Hagman was used in season three as part of the season’s story arc which aired in 2014.

Hagman died on November 23, 2012, at Medical City Dallas Hospital in Dallas following complications from acute myeloid leukemia, after being interviewed for the National Geographic documentary, The ’80s: The Decade that Made Us, which aired in April 2013. In a statement to the Dallas Morning News, Hagman’s family said: “Larry’s family and close friends had joined him in Dallas for the Thanksgiving holiday. He died surrounded by loved ones. It was a peaceful passing, just as he had wished for.” The New York Times described him as “one of television’s most beloved villains”.