Jack Dee was the youngest of three children born to Rosemary A. (née Stamper) and Geoffrey T. Dee, after Joanna Innes Dee and David Simon Innes Dee. Jack was born in Bromley, Kent, and grew up in nearby Petts Wood before moving with his family to Winchester when he was young. His Father, Geoffrey, was a printer and his mother, Rosemary, was the daughter of two unsuccessful repertory actors, Henry Lionel Pope Stamper (1906–1985) and Edna May Howard Innes (1904–1969).

Dee met Susan Jane Hetherington in 1986, when he was working as a waiter in Fulham and she was a receptionist at a nearby hotel. They married in Winchester, Hampshire, in 1989. Together, they have four children.

In his twenties, Dee worked at the Ritz in London and started drinking heavily. He attended church and attempted to become a priest. After he realised that was not for him he gave it up, and never quit drinking, although he would later describe his condition as "alcohol abuse" rather than alcoholism, which was the diagnosis at the time. Since the 1990s, he has advertised John Smith's Bitter, becoming known as "the midget with the widget". Following his appearance on Celebrity Big Brother, he had a relapse, though did not attend AA meetings because he did not want paparazzi photographing him leaving the meetings.

In 1996, he starred alongside Jeremy Hardy in Jack and Jeremy's Real Lives, a collection of mockumentaries similar to their previous collaboration, Jack And Jeremy's Police 4. Each episode would focus on the pair playing bizarre characters from a particular profession. Shot on film and featuring no laugh track, the show failed to catch on. After three episodes it was moved to air after midnight. The pilot featured Sacha Baron Cohen being electrocuted. Aside from his successful stand-up career, Dee has played starring roles and guest appearances in television series. He played the part of Doug Digby in the Grimleys pilot (1997) before the role was recast for the series, and made guest appearances on such programmes as Silent Witness, Dalziel and Pascoe and Jonathan Creek.

In 2001, he won Celebrity Big Brother (then linked to fundraising for Comic Relief). During evictions, he dressed up in a tweed jacket and cap and held his packed suitcase, hoping to be voted out. During the eviction of another housemate he briefly absconded to sneak a quick kiss with his wife. He also escaped for several hours at night-time. He has subsequently said that he dislikes the treatment of the housemates by the show and its producers, and has refused all permission for any of the clips to be shown again.

In 2004, he played the role of Steven Sharples MP the self-styled 'Deputy Home Secretary' alongside Warren Clarke and Dervla Kirwan in The Deputy. Dee's performance was praised, though the film itself received a lukewarm response. Later that year he starred in another one-off drama, Tunnel of Love. He was the Celebrity advocate in Britain's Best Sitcom for Fawlty Towers and presented an hour-long documentary about the series.

In 2005, he co-hosted Comic Aid, a one-off gathering of comedians that aimed to raise money for the Asian Tsunami Appeal. In May of the same year he appeared on the "Star in a Reasonably-Priced Car" segment of the BBC Two series Top Gear, achieving a lap time of 1:53.5 (52nd on the Suzuki Liana leader board). His most recent series Lead Balloon, which he also co-wrote, began on BBC Four on 4 October 2006. Described as "Britain's answer to Curb Your Enthusiasm", Lead Balloon sees Dee play the semi-biographical role of Rick Spleen. A second series of eight episodes was commissioned and was broadcast on BBC Two in 2007, with a third series debuting on Thursday 13 November 2008. A fourth series finished on the BBC on 5 July 2011. He also starred as Harry in the 2005 film Short Order.

In 2007, the Daily Express reported that he was in negotiations with publishers to release his autobiography. He signed with Doubleday in 2008 and the book, Thanks For Nothing: The Jack Dee Memoirs, was released in October 2009, along with an audiobook of the same title which he narrates. According to Dee, "it's really the story of how I got into comedy... It's kind of an autobiography but isn't, as it stops about 25 years ago. It goes right up to the first time I do stand up."

In 2008, Dee took part in the 15th anniversary special of Shooting Stars where he replaced Will Self as captain of Team A. The show aired on 30 December 2008 on BBC2. Dee returned as team captain in series 6 of Shooting Stars on 26 August 2009, and again for the 7th series. Over Christmas 2009, Dee played the role of John Tweedledum in The News at Bedtime.

In February 2009, Dee and several other entertainers wrote an open letter to The Times supporting Bahá'í Leaders, then on trial in Iran.

In 2010, Dee took part in Channel 4's Comedy Gala, a benefit show held in aid of Great Ormond Street Children's Hospital, filmed live at the O2 Arena in London on 30 March. In 2013, Dee joined Dara Ó Briain, Chelsee Healey, Greg James, Mel C and Philips Idowu in Through Hell and High Water, a Comic Relief challenge which involved British celebrities canoeing the most difficult rapids of the Zambezi River. They raised more than £1 million for the charity.