Steven O'Neill trained at the Royal Central School of Speech and Drama and has had an extensive theatre and television career. On TV, he has appeared in Goodbye My Love (Granada), Kavanagh QC (Carlton Television), My Family, Friends and Crocodiles, Sensitive Skin, Fear of Fanny, Olivier Twist, Garrow's Law and M.I. High, all for the BBC. He also appeared as the recurring character of the reverend in Eastenders. Most recently, Steven appeared in The Frankenstein Chronicles for ITV, The Enfield Haunting for Eleven Film Ltd/BSkyB and Liar, also for ITV.
Some of Steven's theatre credits include A Midsummer Night's Dream with the Royal Shakespeare Company, Hamlet and Twelfth Night with Birmingham Repertory Theatre, David Copperfield at the West Yorkshire Playhouse, The Rat Trap at Finborough Theatre, Indian Ink at Salisbury Playhouse, A Midsummer Night's Dream at Zurich Opera House, Hound of the Baskervilles with Oldham Coliseum, and Two Little Boys at Nottingham Lakeside Theatre.