Gibbons was born in 1965 in Exeter, Devon, and raised on a farm with two other sisters. Her parents divorced when she was young. At 22, she moved to Bath, then Bristol to pursue her singing career, where she met Geoff Barrow, her future collaborator in Portishead. She sings in the contralto range.
With Adrian Utley, Gibbons and Barrow released the first Portishead album Dummy in 1994 and have produced two other studio albums, a live album, and various singles in the years since. She has also collaborated on a separate project with former Talk Talk bassist Paul Webb (Rustin Man). Before she joined Geoff Barrow in Portishead, she had auditioned for the singer's slot in .O.rang, the group formed by Webb after Talk Talk's late-Eighties departure from EMI, but Portishead's sudden success pre-empted matters. In October 2002, they released the album Out of Season in the United Kingdom. The album peaked at number 28 in the UK Albums Chart. It was released in the United States a year later.
In June 2013, Gibbons announced plans for a new solo album with Domino Records. She contributed vocals to a cover of the song "Black Sabbath" by the British metal band Gonga, entitled "Black Sabbeth", released 24 April 2014.