While attending a Sixth Form College in Luton, Arnold became friends with director Danny Cannon. Cannon initially created short films for which Arnold was asked to write the music. The two made their respective major film debuts with The Young Americans. "Play Dead", a song from the film with singer Björk, charted No. 12 in the UK. The following year he scored Stargate and Last of the Dogmen, with excerpts from the former ranking third in the most commonly used soundtrack cues for film trailers.
Arnold then composed music for Stargate director Roland Emmerich's next two movies, Independence Day and Godzilla, as well as four movies for director John Singleton. In addition, he has scored various comedies, dramas, and nineteenth-century period pieces, as well as providing music for several British television shows including the 2000 remake of Randall and Hopkirk (Deceased) and Little Britain. During film production, his compositions are conducted by Nicholas Dodd. In 2010, he composed the music for Come Fly With Me, a British television series from the producers of Little Britain.
He is a member of the British Academy of Songwriters, Composers and Authors (BASCA). On Thursday 29 November 2012, Arnold received an honorary degree from University of West London. Now a university honorary, he will work closely with the University in particular London College of Music, a faculty within the institute. In 2014, he appeared as himself in The Life of Rock with Brian Pern.
