Barratt was born in Leeds. He adopted his middle name as his surname to distinguish himself from reporter Julian Pettifer. He attended the University of Reading.
Barratt stars as the character Howard Moon opposite Noel Fielding's Vince Noir in the comedy series The Mighty Boosh. Howard labels himself a "jazz maverick" and claims to be a multitalented intellectual, calling himself a "man of action", but he is actually unsuccessful in his literary and romantic ventures. He is unpopular with many of the characters, including Mrs. Gideon (who always forgets his name), Bob Fossil (who often uses Howard as a puppet for his bizarre schemes), and Bollo (who often says his name wrong or ignores him completely). Barratt composes all of the music for the series, which includes a variety of genres such as rap, heavy metal, and psychedelic rock.
Barratt has had parts in other dramas, often alongside his Mighty Boosh partner Noel Fielding. He starred as Dan Ashcroft, a frustrated magazine writer, in the Channel 4 media satire Nathan Barley, and appeared in the surrealistic black comedy series Asylum alongside Simon Pegg and Jessica Stevenson, who wrote and starred in Spaced. The character of Brian Topp in Spaced was written for Barratt, but eventually went to Mark Heap. Barratt played Jackson, a musician, in How Not to Live Your Life. He starred in the "Freelance Scientist" commercial for Metz alcopop. He appeared as The Padre in the spoof horror series Garth Marenghi's Darkplace. He also starred in (and was a writer for) the 1998 sketch show Unnatural Acts, alongside Fielding. Before this, Barratt was involved in TV series The Pod with friend Tim Hope, about a fictional techno band called The Pod. The show was unusual as everything was animated except for the heads of Barratt and Hope. He also appeared in the 2001 film Lucky Break.
Barratt has recently completed his directing début for Warp Films with theatre director Dan Jemmett. Curtains is set in a Norfolk seaside town. It is a dark comedy about a Punch and Judy man. In 2012, Barratt directed his first music video, for the song "All of Me" by Tanlines. He can be heard as the voiceover on many adverts, such as More Th>n Car, House and Pet insurance, and the Directgov advert. He appeared in the music video for Mint Royale's "Blue Song", alongside Noel Fielding, Nick Frost, and Michael Smiley. In 2010, Barratt took part in Sky Comedy's Little Crackers. He wrote and directed a 15-minute film based on his teen band, Satan's Hoof. On 12 March 2011, he made a brief appearance as Heathcliff in Noel Fielding's "Wuthering Heights" dance on the Let's Dance for Comic Relief finale. He also narrated the 2011 documentary Seven Dwarves.
In 2012, Barratt appeared in the miniseries Treasure Island on Sky1, as well as narrating the BBC Two documentary The Tube. He also had a part as an art teacher in the BBC drama White Heat. In 2013, he appeared in the fifth series of Being Human, playing a werewolf named Larry. He also narrated the BBC Two documentaries The Route Masters: Running London's Roads and The Fifteen Billion Pound Railway. In April 2014, he collaborated with Julia Davis and Joe Frank on Frank's radio show "Isolation," which was broadcast as part of KCRW's UnFictional series.
In April 2016 he starred as Maurice Flowers in the Channel 4 series, "Flowers", a 6 part dark comedy mini series which follows the eccentric and dysfunctional members of the Flowers family. He plays the title character in the film Mindhorn, which was released onto Netflix May 12, 2017, which he co-wrote with Simon Farnaby.
From 3 June to 9 July 2011, Barratt played the Mayor in a production of Nikolai Gogol's classic comedy The Government Inspector at the Young Vic Theatre. In October 2012, he returned to the stage in Lucy Kirkwood's play NSFW at the Royal Court.
Barratt is an accomplished musician, and played guitar for Little Chief during their European tour. He claims to be a "jazz fusion fanatic". He was in a band called Groove Solution in the early 1990s with Dave Westlake. He has also played with Chris Corner in IAMX.
Barratt is in a relationship with comedian Julia Davis. They are the parents of twins Arthur and Walter, born 25 June 2007. Barratt is known to be shy, quiet, and self-deprecating. Unlike his comedy partner Noel Fielding, he prefers not to appear on comedy quiz shows, stating that he would rather stay at home and read a book.2010 The Mighty Boosh won Best Live Show with Future Sailors at the Shockwaves NME Awards 2010.
2009 The Mighty Boosh won Best TV Show at the Shockwaves NME Awards 2009
2008 The Mighty Boosh won Best TV Show at the Shockwaves NME Awards 2008.
2007 The Mighty Boosh won Best TV Show at the Shockwaves NME Awards 2007.
2001 The Boosh, first on London Live, then on Radio 4.
2000 Arctic Boosh won the Barry Award at the Melbourne International Comedy Festival
1999 Perrier nominee with Noel Fielding as Arctic Boosh
1998 Perrier Best Newcomer winner with Noel Fielding as the double act The Mighty Boosh
1995 Winner of BBC New Comedy Awards
1995 Open Mic Awards, Edinburgh