Duncan was born in Helensburgh, Scotland and trained at the Royal Scottish Academy of Music and Drama.
His theatre credits in the West End include: Marguerite, Anything Goes, Calamity Jane, Kiss Me, Kate, The Secret Garden, Spend Spend Spend, Copacabana, The Phantom of the Opera, Chess and Evita. For the Royal National Theatre: Love’s Labour’s Lost, Anything Goes, Lady in the Dark and The Inheritor, and for the Royal Shakespeare Company: The Secret Garden (Stratford and West End).
Other theatre includes: Chitty Chitty Bang Bang (tour); Kiss Me, Kate (tour); Wait Until Dark (Denny Civic Theatre, Dumbarton); The Thrie Estaites (the Scottish Theatre Company); Camelot (Liverpool Playhouse); Let ‘Em Eat Cake (Opera North); Madame Zoyka (Troubadour Theatre); La Cenerentola (Vienna Festival and Royalty Theatre); Jesus Christ Superstar, The Mikado and She Loves Me (Theatre Royal, Perth); Kes (Theatre Royal, York); Tomfoolery (Players’ Theatre); Trial by Jury and The Little Matchgirl (Orange Tree Theatre); and Doctor Dolittle (Apollo Hammersmith).
Other productions include: A Terrible Beauty (The Old Vic); Robin and the Seven Hoods and Sleeping Beauty (both at the Venue).
For television: Spectrum, Kiss Me, Kate, Good News for Ne’er Day, Copacabana the Inside Story, Children in Need, Pebble Mill and A Christmas Message.
Recordings include: Marguerite, The Secret Garden, Spend Spend Spend, Doctor Dolittle, Copacabana, My Fair Lady, Fiddler on the Roof and Lady in the Dark.