Chapman was born at the Stoneygate Nursing Home, Stoneygate, Leicester. He was educated at Melton Mowbray Grammar School and studied medicine at Emmanuel College, Cambridge. He was also an avid fan of radio comedy from an early age, becoming especially drawn to that of The Goon Show. In the introduction to Chapman's (2005/2006) posthumous anthology, Jim Yoakum notes that "the radio shows didn't necessarily make him laugh. Only a select few got chuckles from young Chapman including Frankie Howerd, the team of Jimmy Jewel and Ben Warriss, It's That Man Again, Educating Archie, Take It From Here and Much-Binding-in-the-Marsh. 'I especially liked Robert Morton, although no one else seemed to like him very much. He would do things like tell jokes the wrong way around and switch punch lines. He was obviously a very good comedian and was ahead of his time. The appearance of incompetence was wonderful. He was one of my heroes.' But the show that truly astounded Graham, and was a major influence on his comedy was The Goon Show" (p.xvii). Chapman states "from about the age of seven or eight I used to be an avid listener of a radio programme called The Goon Show. In fact, at that stage I wanted to be a Goon" (p. 23).

At Cambridge, he began writing comedy sketches with fellow student and future Python costar John Cleese. Chapman qualified as a doctor at the Barts and The London School of Medicine and Dentistry, but never practised medicine professionally. While at Cambridge, Chapman joined Footlights. His fellow members included Cleese, Tim Brooke-Taylor, Bill Oddie, Tony Hendra, David Hatch, Jonathan Lynn, Humphrey Barclay, and Jo Kendall. Their revue, A Clump of Plinths, was so successful at the Edinburgh Festival Fringe that they renamed it Cambridge Circus, and took the revue to the West End in London and later New Zealand and Broadway in September 1964. The revue appeared in October 1964 on The Ed Sullivan Show.

Before Python

Cleese and Chapman wrote professionally for the BBC during the 1960s, primarily for David Frost, but also for Marty Feldman. Chapman also contributed sketches to the BBC radio series I'm Sorry, I'll Read That Again and television programmes such as The Illustrated Weekly Hudd (starring Roy Hudd), Cilla Black, This is Petula Clark, and This Is Tom Jones. Chapman, Cleese, and Brooke-Taylor then joined Feldman in the television comedy series At Last the 1948 Show. Here Chapman displayed a gift for deadpan comedy (particularly evident in the sketch "The Minister Who Falls to Pieces") and for imitating various British dialects. Chapman, and on occasion Cleese, also wrote for the long-running television comedy series Doctor in the House. Chapman also co-wrote several episodes with Bernard McKenna and David Sherlock.

Monty Python

In 1969 Chapman and Cleese joined Michael Palin, Terry Jones, Eric Idle and American artist Terry Gilliam for the BBC television comedy series Monty Python's Flying Circus. He most often played characters with personalities close to his own: outwardly calm, authoritative figures barely concealing a manic unpredictability.

In David Morgan's 1999 book Monty Python Speaks, Cleese asserted that Chapman ... although officially his co-writer for many of their sketches ... contributed comparatively little in the way of direct writing. Rather, the Pythons have said that his biggest contribution in the writing room was an intuition as to what was funny. John Cleese said in an interview that one of Chapman's great attributes was "his weird takes on things." In writing sessions Chapman "would lob in an idea or a line from out of left field into the engine room, but he could never be the engine", Cleese said. In the Dead Parrot sketch, written mostly by Cleese, the frustrated customer was initially trying to return a faulty toaster to a shop. Chapman would ask "How can we make this madder?", and then came up with the idea that returning a dead Norwegian Blue parrot to a pet shop might make a more interesting subject than a toaster.

Chapman played the lead roles in the troupe's first two narrative feature films: Monty Python and the Holy Grail and Life of Brian. Cleese complimented his writing partner by saying that he was "very possibly the best actor of all of us".

Final years

In the late 1970s, Chapman moved to Los Angeles, where he guest-starred on many U.S. television shows, including Hollywood Squares, Still Crazy Like a Fox, and the NBC sketch series The Big Show. Upon returning to England he became involved with the Dangerous Sports Club (an extreme sports club which introduced bungee jumping to a wide audience). He began a lengthy series of U.S. college tours in the 1980s, where he would tell the audience anecdotes about Monty Python, the Dangerous Sports Club, Keith Moon, and other subjects. His memoir, A Liar's Autobiography, was published in 1980 and, unusual for an autobiography, had five authors: Chapman, his partner David Sherlock, Alex Martin, David Yallop and Douglas Adams, who in 1977 was virtually unknown as a recent graduate fresh from Cambridge. Together they wrote a pilot for a TV series, Out of the Trees; it was aired in 1975, but never became a series. They also wrote a show for Ringo Starr, which was never made. Chapman mentored Adams, but they later had a falling out and did not speak for several years. It took years of planning and rewriting before he secured the funds to create Yellowbeard; The movie was finally released in 1983.

In 1988, Chapman appeared in the Iron Maiden video, "Can I Play with Madness". His last project was to have been a TV series called Jake's Journey. Although the pilot episode was made, there were difficulties selling the project. Following Chapman's death, there was no interest. Chapman was also to have played a guest role as a television presenter in the Red Dwarf episode "Timeslides", but died before filming was to have started.

In the years since Chapman's death, despite the existence of the "Graham Chapman Archive", only a few of his projects have actually been released. One of these projects is a play entitled O Happy Day, brought to life in 2000 by Dad's Garage Theatre Company in Atlanta, Georgia. Cleese and Palin assisted the theatre company in adapting the play.

Chapman was a tall (6'2"/1.88 m), craggy pipe-smoker who enjoyed mountaineering and playing rugby.

Chapman was an alcoholic from his time in medical school. His fellow Pythons noted he felt he needed a drink or two to "face the world" and at times would forget in the afternoon material that had been written the same day. His drinking also affected his performance on the TV recording set as well as on the set of Holy Grail, where he suffered from withdrawal symptoms including delirium tremens. He stopped drinking on Boxing Day 1977, having just irritated the other Pythons with an outspoken (and drunken) interview with the New Musical Express. Before going sober, Chapman jokingly referred to himself as the British actress Betty Marsden, possibly because of Marsden's oft-quoted desire to die with a glass of gin in her hand. John Cleese used Marsden's name in his eulogy at Chapman's memorial service.

Chapman kept his sexuality a secret until the 1970s, when he came out as homosexual on a chat show hosted by British jazz musician George Melly, becoming one of the first celebrities to do so. Several days later, he came out to a group of friends at a party held at his home in Belsize Park, where he officially introduced them to his partner, David Sherlock, whom he had met in Ibiza in 1966. Chapman later told a story in his college tour that when he went public, a member of the television audience wrote to the Pythons to complain that she had heard a member of the team was gay, adding that the Bible said any man who lies with a man should be taken out and stoned. With fellow Pythons already aware of his sexual orientation, Eric Idle replied, "We've found out who it was and we've had him shot." In his book Graham Crackers, Chapman said that this took place just before John Cleese left the show, and he wondered what the woman thought about his disappearance after getting Idle's response.

Chapman was a vocal spokesman for LGBT rights, and in 1972 he lent his support to the fledgling newspaper Gay News, which publicly acknowledged his financial and editorial support by listing him as one of its "special friends". In 1971, Chapman and Sherlock adopted John Tomiczek as their son. Chapman met Tomiczek when the teenager was a runaway from Liverpool. After discussions with Tomiczek's father, it was agreed that Chapman would become Tomiczek's legal guardian, and Tomiczek later became Chapman's business manager. Tomiczek died of a heart attack in 1992.

Among Chapman's closest friends were Keith Moon of The Who, singer Harry Nilsson, and The Beatles' Ringo Starr.

Chapman died on 4 October 1989 after suffering from throat cancer and secondary spinal cancer. He had several chemotherapy appointments and tumor removal surgeries within the last year of his life, and at one point, he ended up confined to a wheelchair. By September 1989 the cancer was declared terminal. He filmed scenes for the 20th anniversary of Python that month, the last time he would appear on screen, but was taken ill again on 1 October. Present when he died in a Maidstone hospital including his brother, sister-in-law, partner David Sherlock, and his former Python fellows John Cleese and Michael Palin, who had to be led out of the room to deal with their grief. Terry Jones and Peter Cook had visited earlier that day. Chapman's death occurred one day before the 20th anniversary of the first broadcast of Flying Circus; Jones called it “the worst case of party-pooping in all history."

John Cleese stated in his show 'A Ludicrous Evening with John Cleese ... or How to Finance Your Divorce, Year Two'.. that Graham Chapman died of throat cancer cause by smoking a pipe much of his life. He paid homage to Chapman througout his performance.

Memorial service

The five surviving Python members decided to stay away from his private funeral, to prevent it becoming a media circus and to give Chapman’s family some privacy. They sent a wreath in the shape of the famous Python foot with the message “To Graham from the other Pythons. Stop us if we’re getting too silly”. They held a private memorial service in St Bartholomew's Hospital in London on the evening of 6 December 1989, with a chorus of the Chinese version of the hymn "Jerusalem" (" Bling me my speal, oh crowds unford, bling me my chaliot of file"). Cleese delivered his eulogy, which began as follows:

Cleese continued after a break from laughter in the audience, claiming Chapman had whispered in his ear the night before, when he was writing the speech, saying:

Palin also spoke, saying that he liked to think that Chapman was there with them all that day ... "or rather, he will be in about 25 minutes," a reference to Chapman's habitual lateness when they were all working together. Idle, choking back tears, stated of Chapman that he had thought that Palin talked too much and had died rather than listen to him any more. He also led other surviving Python members along with Chapman's family and close friends in a rendition of "Always Look on the Bright Side of Life" from the film Monty Python's Life of Brian. Not to be outdone by Cleese, Idle was heard saying during the song's close: "I'd just like to be the last person at this meeting to say 'fuck'. Thank you very much, God bless you, Graham."

Burial

On 31 December 1999, Chapman's ashes were rumoured to have been "blasted into the skies in a rocket". In reality, however, Sherlock scattered Chapman's ashes on Snowdon, North Wales on 18 June 2005.

Legacy

After Chapman's death, speculation of a Python revival inevitably faded. Eric Idle said "We would only do a reunion if Chapman came back from the dead. So we're negotiating with his agent." Subsequent gatherings of the Pythons have included an urn said to contain Chapman's ashes. At the 1998 Aspen Comedy Arts festival, the urn was "accidentally" knocked over by Terry Gilliam, spilling the "ashes" on-stage. The cremains were then removed with a dust-buster.

Asteroid 9617 Grahamchapman, named in Chapman's honour, is one of six asteroids carrying the names of members of the Monty Python comedy troupe.

In 1997, David Sherlock allowed Jim Yoakum to start the Graham Chapman Archives. Later that year, the novel Fuzzy Memories, Silly Bits, and Outright Lies was released. It is a semi-sequel to A Liar's Autobiography, with Chapman works compiled by Yoakum. Ojril: The Completely Incomplete Graham Chapman, a collection of previously unpublished material, was released in 1999. It contains scripts Chapman wrote with Douglas Adams and others, such as "Our show for Ringo Starr, a.k.a. Goodnight Vienna". In 2005 Calcium Made Interesting: Sketches, Letters, Essays & Gondolas was published. At one time, the script for "Out of the Trees", written by Chapman and Adams in 1975 (and later extensively rewritten by Chapman with Bernard McKenna), was online. Jim Yoakum had it removed, to the disappointment of co-writer Adams, who had made no objections to it being there.

Recordings of Graham Chapman's college tours in the 1980s have been released over the years. The CD A Liar Live was delayed several times, but was released as A Six Pack of Lies in 1997. Other college tours also came out on CD, such as Spot the Loony in 2001. A DVD of the tours (Looks Like a Brown Trouser Job) was released in 2005. The single episodes for "Out of the Trees", which was wiped but later recovered on an early home video system, and "Jake's Journey" still have not been released.

In 2004 there was talk of a movie about Chapman's life, to be called Gin and Tonic, by Hippofilms in cooperation with Jim Yoakum. Auditions were held in March 2004 in California, but the project has been officially abandoned. Its website is no longer online and the Internet Movie Database page has been deleted; the Graham Chapman Archive's website has disappeared as well.