In 1967 Marshall was working as a film editor at Signal Films (part of EUE/Screen Gems) in Berwick St London. He left to be a commercials producer at CDP (Collett, Dickenson & Pearce).
Before producing feature films, with help from CDP, he and Alan Parker started the TVC production Company Alan Parker productions. Marshall has worked as producer in feature films that have been directed by Parker from Bugsy Malone up to Angel Heart. After Angel Heart, Marshall decided to leave working with Parker to focus on other work.