Guy Pratt was born on 3 January 1962, in a flat above a shop on the street The Cut, in Lambeth, South London, England, United Kingdom. His father, Mike Pratt, was an actor, songwriter and screenwriter but died when Guy was 14. Pratt worked for a while as a graphic designer, but then decided to concentrate on a music career. In the late 1970s, Pratt was in a band based in Southend-On-Sea called Speedball, which released a single on NO PAP1 Records called ‘No Survivors’. In 1981, aged 19, Pratt was asked to tour with Icehouse. Two years later as a member of Icehouse he supported David Bowie on his Serious Moonlight Tour, which was Bowie’s longest, largest, and most successful concert tour. A support slot at a 1984 David Gilmour solo concert led to a stint with Pink Floyd. He also spent some time in Los Angeles where he played with Madonna and Michael Jackson.

In 1986 the Smiths’ bassist Andy Rourke was arrested on drug possession charges shortly before the band was scheduled to leave for its North American tour in support of The Queen Is Dead. Expecting that Rourke would thus be denied work visas for the U.S. and Canada, the band’s guitarist, Johnny Marr, asked Pratt to step in. He spent nearly two weeks with Rourke and the band, learning bass lines and rehearsing, but shortly before the band was to leave Britain Rourke received his visas, and there was no need for Pratt to go.

Pratt came to prominence when he was chosen to play bass for Pink Floyd’s post-Roger Waters A Momentary Lapse of Reason Tour in 1987–90, and The Division Bell Tour in 1994. He co-performed the lead vocals on “Run Like Hell”, “Another Brick in the Wall, Part 2”, “Us and Them” and “Comfortably Numb” with Gilmour during the live shows. He also played bass on several tracks on The Division Bell. Tony Levin had performed all of the bass parts on A Momentary Lapse of Reason; Pratt replaced him on the later tour owing to Levin’s unavailability. Pratt also toured as part of Gilmour’s On an Island Tour backing band, alongside another Pink Floyd member (and his father-in-law), Richard Wright.

Pratt played his fretted 5-string and fretless 4-string Status headless basses, the amber Spector NS2, the burgundy mist “Betsy” 1963 Jazz Bass and two Precision Basses (a 2-colour sunburst 1958 and a “single-coil pickup” butterscotch blonde 1951) during the Pulse concerts in 1994.

Pratt married furniture designer Gala Wright, daughter of Pink Floyd keyboardist Richard Wright, in 1996 in the Royal Borough of Kensington and Chelsea, London. The couple have a son, but subsequently divorced.

Pratt played bass on Gary Moore’s Dark Days in Paradise tour in 1997.

Pratt and Jimmy Cauty released a single “I Wanna 1-2-1 With You” as Solid Gold Chartbusters in 1999; Pratt and Cauty (a founder of the Orb) later teamed up with the other original member of the Orb, Alex Paterson, to form Transit Kings.

Pratt’s one-man music and comedy show, My Bass & Other Animals, debuted in August 2005 at the Edinburgh Festival Fringe; this led to his book of the same name, published in May 2007. Pratt spent 2011 performing stand-up in Switzerland, Australia, and at the Edinburgh Fringe, as well as on a South American tour playing bass guitar for Dominic Miller.

In April 2010, Pratt joined Argentine band The End Pink Floyd, with Durga McBroom and Jon Carin, in Buenos Aires, Argentina. Pratt joined the Australian Pink Floyd Show on stage on 13 June 2011 for the Hampton Court Palace Festival for the song “Run Like Hell”. He joined the UK Pink Floyd cover band Brit Floyd on stage on 9 November 2013 as a special guest during the Liverpool leg of their Pulse tour. He performed on the songs “One of These Days”, “Comfortably Numb” and shared lead vocals with the band’s lead singer Damian Darlington during the finale of “Run Like Hell”.

In 2018, Pratt and others formed a new band, Nick Mason’s Saucerful of Secrets, to perform Pink Floyd’s early psychedelic material. Along with Pratt, the band comprises Pink Floyd drummer Nick Mason, former Blockheads guitarist Lee Harris, vocalist and guitarist Gary Kemp of Spandau Ballet, and Pratt’s collaborator keyboardist Dom Beken. The band toured Europe and North America in 2018 and 2019, with a third tour postponed to 2021 due to the COVID-19 pandemic. In September 2020, they released a live album and film, Live at the Roundhouse.

In March 2019 he became engaged to the children’s author Georgia Byng.

Also in 2019, he was announced as the general election candidate for the Renew Party in Brighton Kemptown.