Duncan's theatre work includes:

Labour of Love (Michael Grandage), Love In Idleness (Menier, West End), Privacy (Public Theater, New York), The Tempest (St Ann’s Warehouse, New York), Another World (National Theatre), Hangmen (Royal Court/Wyndham’s), The Bodyguard (Adelphi Theatre/UK Tour/Worldwide), Committee, Saint Joan, The Shakespeare Trilogy, One Night In Miami, Privacy and City of Angels (Donmar Warehouse), 28 Days Later, Doctor Strangelove and Star Wars (Secret Cinema), Impossible (Noel Coward);Harry Enfield and Paul Whitehouse - Legends! (UK Tour), The Hairy Ape, A Flea In Her Ear, The Tempest, The Real Thing, The Norman Conquests and All About My Mother (Old Vic), The Mentalists (Wyndham’s Theatre), Ghost The Musical (Germany), John Bishop – Supersonic (UK Tour), Still Game Live (Glasgow Hydro Arena), Shrek The Musical (Drury Lane/UK Tour), War Horse Prom (Royal Albert Hall), Albion (Bush), Derren Brown – Infamous (Palace Theatre/UK Tour), Macbeth and The Flying Dutchman (NI Opera), A Conversation With John Travolta (Drury Lane), Theatre Uncut (Young Vic), Inside Wagner’s Head (Royal Opera House), If Only (Chichester Festival Theatre), Let It Be (West End/UK Tour/Broadway/Worldwide), Strictly Confidential (UK Tour), Catwalk Confidential (Miami/London), Kristina (Royal Albert Hall), The Hairy Bikers Big Night Out (UK Tour), The Norman Conquests (Broadway), Frost/Nixon (Gielgud) and Evita (International Tour).