Mansell is one of the young generation of film music. His music is dominated by electronic elements, some of which are combined with classical elements, such as. Known in his score to Requiem for a Dream, for which he collaborated with the Kronos Quartet
He began his career as a singer and guitarist of the band Pop Will Eat Itself. For film music, he came upon his friend, director Darren Aronofsky. Mansell set to music for Aronofsky whose debut Pi direct it, their second collaboration: Requiem for a Dream. The score has been widely received positively and once again received additional notoriety when the Requiem Lux Aeterna main theme for the trailer for The Lord of the Rings: The Two Towers was used in an orchestrated version. The title was later also for the trailers for Zathura - A Space Adventure, The Da Vinci Code - The Da Vinci Code, Babylon AD used and Sunshine. The music Am Legend used in the trailer for the film I comes from the movie The Fountain and also strongly reminiscent of this score, the title is here Fatal Fantasy of the Music Junkies. Further collaborations with director Aronofsky followed.
Also quite popular was a remix album of the Requiem soundtrack on which involved well-known artists such as, inter alia, Paul Oakenfold, Josh Wink, Jagz Kooner, and Delerium.
Furthermore, Mansell was in the play Starfuckers, Inc. on the album The Fragile Nine Inch Nails the part of the choir.