Mitchell is an English composer best known for his writing and arranging period movie scores for choir and orchestra, though his compositions span a very wide range of styles varying from classical to more contemporary electronic genres such as drum and bass and trip hop.
He also has a reputation for working in a diverse range of world music styles, such as the Tibetan score for Nick Gray's Escape from Tibet in contrast to a country and western pedal steel guitar-based score for Grand Theft Parsons, successful with film music critics at the 2004 Sundance Festival.
His score for the film Trial by Fire won an Ivor Novello Award in 2000 and the BBC period drama The Tenant of Wildfell Hall won Best Score at the Royal Television Society Awards in 1998.
In 2005, Mitchell composed the music for The Call of the Toad, written by Günter Grass and directed by Robert Gliński.
He was commissioned to write the score for one-man theatre show Ousama with Nadim Sawalha directed by Corin Redgrave at the Brixton Shaw Theatre, and a jazz suite for the Francis Bacon Retrospective Exhibition at the Tate Britain in 2008.