Born in Aberdeen, Scotland, he grew up in Preston, England. Garden was educated at Repton School, and studied medicine at Emmanuel College, Cambridge, where he joined the prestigious Cambridge University Footlights Club (of which he became President in 1964), and performed with the 1964 Footlights revue, Stuff What Dreams Are Made Of at the Edinburgh Festival Fringe.
Garden qualified in medicine at King's College London, but has never practised. Asked how he justified making jokes rather than saving lives, he answered:
I don't think I would have done it as well. It's an interesting question – whether you've contributed more to the vast store of human enjoyment by doing comedy or by being a doctor, but the answer for me is that I don't think I would have been as successful or as happy being a doctor.
Garden was co-writer and performer in the classic BBC radio comedy sketch show, I'm Sorry, I'll Read That Again, in the late 1960s. Garden was studying medicine during the early seasons of I'm Sorry, I'll Read That Again, and this commitment made it difficult for him to be a member of the cast during the third season because of a midwifery medical course in Plymouth. However, he continued sending scripts for the radio show by mail – and rejoined the cast upon his return to his medical studies in London. On several occasions his medical qualifications are lampooned; in the 25th Anniversary Show, David Hatch asks him if he is still a writer. Garden: "Here's something I wrote this morning". Hatch: "It's a prescription". "Yes," says Garden, "but it's a funny one..."
Garden is a permanent panellist on the long-running BBC Radio improvisation show I'm Sorry I Haven't a Clue in a cast which includes Tim Brooke-Taylor. He also stars in and co-writes, with Barry Cryer, You'll Have Had Your Tea, a direct spin-off of ISIHAC, and has contributed to several books from the series including guides to the game Mornington Crescent.
Garden wrote for and appeared with Barry Cryer and Alison Steadman in the 1989 BBC radio comedy sketch show The Long Hot Satsuma. In 2001 and 2002, Garden wrote for and appeared in the BBC radio comedy sketch show The Right Time, along with Eleanor Bron, Paula Wilcox, Clive Swift, Roger Blake and Neil Innes. He was also script editor for The Hudson and Pepperdine Show.
Garden is chair of the spoof radio game show Beat the Kids. He has also appeared on the UK version of the improvisation television series Whose Line Is It Anyway?, which has a similar format. He was a co-writer of the BBC Radio 4 comedy Giles Wemmbley-Hogg Goes Off, and in 2006, Garden co-devised and appeared on the BBC Radio 4 comedy quiz show, The Unbelievable Truth.
In 2003, Garden wrote the Radio 4 sitcom About a Dog, based on an original idea by Debbie Barham, with a second series in 2007.
Garden has appeared in two of Big Finish's Doctor Who audio dramas playing a parodic character. In Bang-Bang-a-Boom! he plays Professor Fassbinder, a parody of Victor Bergman in Space: 1999. In Max Warp he plays TV presenter Geoffrey Vantage, parodying Top Gear presenter Jeremy Clarkson. He also plays Abbot Thelonious (an alias of the Meddling Monk) in the Eighth Doctor audio play The Book of Kells in 2010, and subsequently returns as a recurring antagonist to the Eighth Doctor.
Garden's best known television work is freeform sitcom The Goodies, which he wrote and performed along with Tim Brooke-Taylor and Bill Oddie from 1970 to 1982. The three appeared in the Amnesty International show A Poke In The Eye (With A Sharp Stick) (during which they sang their hit song "Funky Gibbon"). Garden and Bill Oddie co-wrote many episodes of the television sitcom Doctor in the House, including most of the first series episodes, and all of the second series episodes - as well as co-writing episodes of the subsequent Doctor at Large and Doctor in Charge series. Garden was co-writer and performer in the sketch show Twice a Fortnight with Bill Oddie, Terry Jones, Michael Palin and Jonathan Lynn, and also sketch show Broaden Your Mind with Tim Brooke-Taylor, with Bill Oddie joining the cast for the second series.
In 1982 Garden and Oddie wrote, but did not perform in, a six-part science fiction sitcom called Astronauts for Central which was shown on ITV. The show was set in an international space station in the near future.
Garden was the voice of the title character in Bananaman (1983), in addition to General Blight and Maurice of the Heavy Mob in the children's animated television comedy series, which also featured the rest of the Goodies team. The series parodied comic book super-heroes. Later, Garden wrote for the sitcom Surgical Spirit (1994). Graeme Garden has also presented three series of the BBC's health magazine Bodymatters.
Garden appeared in the political sitcom, Yes Minister in the role of Commander Forrest of the Special Branch in the episode The Death List, as well as appearing as a television presenter in the Doctor in the House episode, Doctor on the Box.
He was a regular team captain on the political satire game show If I Ruled the World. Brooke-Taylor appeared as a guest in one episode and during the game "I Couldn't Disagree More" he proposed that it was high time The Goodies episodes were repeated. Garden was obliged by the rules of the game to refute this statement, and replied, "I couldn't disagree more... it was time to repeat them ten, fifteen years ago."
In 2004, Garden and Brooke-Taylor were co-presenters of Channel 4's daytime game show Beat the Nation, in which they indulged in usual game show "banter", but took the quiz itself seriously. It was notable for its use of a "laugh track" instead of a studio audience. Garden has hosted the quiz game Tell the Truth and presented a series of history programmes, A Sense of the Past for Yorkshire Television.
Garden writes and directs for the corporate video company Video Arts, famous for its training films starring John Cleese.
Garden has a successful stage career, and has acted in several National Theatre productions, as well as London's West End. He has also acted in several BBC Radio 4 comedy drama series, and television drama including Peak Practice and Holby City. He appeared in Bang-Bang-a-Boom!, a spin-off audio drama based on the BBC science fiction television series Doctor Who by Big Finish Productions. Garden appeared with Tim Brooke-Taylor in the theatre production The Unvarnished Truth.
In 1986 he appeared in a production of An Inspector Calls by J B Priestley at the Royal Exchange, Manchester.
Garden wrote a play called The Pocket Orchestra which ran in London in 2006. In August 2006, Garden and Brooke-Taylor joined up to perform at the Edinburgh Fringe in a show which looked back with some nostalgia to their work with the Goodies and in light entertainment.
Garden lives in Oxfordshire with his wife Emma, with whom he has a son, Tom. Garden also has a daughter, Sally, and a son, John, from his previous marriage to Mary Elizabeth Wheatley Grice. His son John "JJ" Garden is the occasional keyboardist for the music group Scissor Sisters, and shares songwriting credit on their 2006 album Ta-Dah. Garden's father, Robert Symon Garden, was an eminent orthopaedic surgeon who created the Garden classification of hip fractures and the Garden screw, used to repair certain hip fractures. R. S. Garden died on 16 October 1982 at the age of 72.
In 2002, Garden suffered an episode of the condition known as Bell's palsy, where the muscles on one side of the face become paralysed. He was able to continue his work commitments and made a full recovery.
Garden was appointed Officer of the Order of the British Empire (OBE) in the 2011 Birthday Honours for services to light entertainment.
Garden is a patron of the disability charity ENRYCH – formerly Ryder-Cheshire Volunteers. The charity works to enable adults with a physical disability to enjoy culture, leisure, learning and sporting opportunities through partnership with a volunteer.