Denis was born in Glasgow. He studied graphic design at Glasgow school of Art before attending the National Film and Television School in Beaconsfield to pursue his interest in cinematography.

“As a kid, I was taken to the cinema every week, so I saw a lot of movies. As I got older I became interested in how they were photographed, how they achieved a visual style and who had filmed them….Cinematographers such as Vilmos Zsigmond and Gordon Willis”

Crossan started his career shooting Music Videos while still at Film School. He then went on to shoot numerous commercials, and through the years he has worked with major directors and advertising agencies, resulting in a number of awards for cinematography, including Cleo, Creative Circle and D&AD awards.

His first feature film credit was Melancolia, an art house thriller set in London and produced by the BFI directed by Andi Engel in 1990. In 1993 he was asked to join The British Society of Cinematographers (B.S.C.). His movie credits include I Know What You Did Last Summer, directed by Jim Gillespie, starring Sarah Michelle Gellar and Ryan Phillippe; Clandestine Marriage, directed by Christopher Miles, starring Nigel Hawthorne and Timothy Spall, which won Best Cinematography Newport Beach Film Festival California 2000; The Hole, directed by Nick Hamm, starring Thora Birch and Keira Knightley; Me Without You, directed by Sandra Goldbacher, starring Michelle Williams, Anna Friel and Kyle MacLachlan; Agent Cody Banks, directed by Harald Zwart, starring Frankie Muniz and Hilary Duff; Pink Panther 2, starring Steve Martin, Andy García, Jean Reno, John Cleese, Alfred Molina and Emily Mortimer. and television episodes 'The Bastard Executioner' for Fox and 'Outlander' for Sony. His latest work includes, the feature film ‘Hitman Redemption' directed by Michael Caton-Jones starring Ron Perlman, Famke Janssen and Richard Dreyfuss and ‘Our Ladies’ for Sony Pictures directed by Michael Caton Jones