Cusick began his career as a classical theatre actor. His first leading roles on stage included: Dorian Gray in "The Picture of Dorian Gray" with Rupert Everett, Hamlet in "The Marovitz Hamlet", and Horner in "The Country Wife". His 1994 performances as Torquato Tasso in the Edinburgh International Festival production of "Torquato Tasso", and Creon in the Citizens' Theatre production of "Oedipus", earned him a commendation at the 1995 Ian Charleson Awards for outstanding performance by a young actor in a classical theatre role.