Born as Stephen Delaney in South London and raised in Kent, Dillane pursued a career in journalism after graduating from the University of Exeter. He has said in interviews that he was not driven to pursue acting and applied to drama school on a whim. He had read an interview with British actor Trevor Eve who had made the switch from architecture to acting and Dillane figured he would give it a try. After completing the two year program at the Bristol Old Vic Theatre School, he adopted the stage name Stephen Dillon and began his career appearing in small roles in TV (i.e., "The Secret Garden", CBS 1987) and features ("Business as Usual" 1987). He went on to become established on the London stage in such productions as Brian Friel's "Dancing at Lughnasa" and "The Beaux Stratagem" (alongside Brenda Blethyn). By then, he had adopted Dillane as his stage name. He triumphed in a Peter Hal staging of "Hamlet" in 1994 and tackled "Uncle Vanya" in 1998.
Now billed as Stephen Dillane, he played Horatio to Mel Gibson's "Hamlet" (1990) and then appeared as one leg of a romantic triangle in David Hare's WWII-era "Heading Home" (1991). After a turn as a journalist covering the conflict in Vietnam in the miniseries "Frankie's House" (A&E, 1993), he was again embroiled in a period romantic triangle in "The Rector's Wife" (PBS, 1994). Dillane co-starred with Denis Leary and Sandra Bullock in the unsuccessful "Two If By Sea/Stolen Hearts" (1996) and went on to romance Sophie Marceau in "Firelight" (1997) before essaying a mysterious, married painter who falls for an American (Victoria Foyt) in Henry Jaglom's "Deja Vu" (1998). In 1999, he starred in the festival film "The Darkest Light" as a father whose child has cancer. In 2000, Dillane appeared in a British miniseries production of "Anna Karenina" which was nominated for several awards. In 2001, he had a supporting roel in the thriller "Spy Games" starring Brad Pitt and Robert Redford. Next Dillane took on another supporting role in the thriller "The Truth About Charlie" (2002), a remake of the 1963 classic "Charade," and turned in an appropriately restrained and haunted performance as Virginia Woolf's husband Leonard in "The Hours" (2002).