Sadier was working as a nanny when she met McCarthy leader Tim Gane at a gig in Paris during the late 1980s. Sadier was disillusioned with the rock scene in France, and soon moved to London to be with Gane and to pursue her career. She had contributed vocals to McCarthy’s third and final album. The band broke up in 1990 and she and Gane immediately formed Stereolab. For the first incarnation of the band, they enlisted ex-Chills bassist Martin Kean, drummer Joe Dilworth and Gina Morris on backing vocals.
While Tim Gane has written the bulk of the music in Stereolab, it is Sadier’s singsong, alto vocals and often revolutionary lyrics (both in English and French) that have become trademarks of the band’s sound. Sadier also plays keyboards, percussion, guitar (she’s left-handed) and trombone.
In 1996, Sadier formed the spin-off band Monade with Pram’s Rosie Cuckston.
Sadier has contributed vocals to various other groups and projects, at times along with the late Stereolab member Mary Hansen. Among her contributions were, adding French backing vocals on To The End, a top 20 hit for Blur in 1994. In 1995, Sadier had recorded the Serge Gainsbourg/Brigitte Bardot song “Bonnie and Clyde” with Luna. She and Hansen had contributed vocals to the recordings of The High Llamas (the project of sometimes-Stereolab member Sean O’Hagan). In 2001, Sadier sang on “Sol y Sombra” on Fugu’s Fugu 1 LP on Minty Fresh Records. In 2002, Sadier sang the chorus on New Wave from Common’s album Electric Circus. She sang lead vocals on Haiku One from Sigmatropic’s 2004 album Sixteen Haiku & Other Stories which was an album based on the poetry of Greek poet George Seferis. In 2009 the French label Deux Mille released an ep which features Laetitia Sadier singing with momotte, a band out of Toulouse.
Sadier also wrote and sang the lyrics to the track Quick Canal by Atlas Sound for the 2009 release Logos.
In 2010 she released a solo album called The Trip.
While she spent most of her formative years in France, Sadier’s family travelled extensively and she lived briefly in the US as a child.
After many years together (they remained unmarried), Sadier and Tim Gane split up in 2004, but they continued to work together in Stereolab until the band’s hiatus in 2009. They have a child, Alex, born in 1998.