The Scotsman began his career as an actor in the mid-1970s, appearing in revues at the Edinburgh Festival and later in the premiere of "The Slab Boys" by John Byrne. Doyle made his feature acting debut in Hugh Hudson's Oscar-winning "Chariots of Fire" (1981). In 1987, Branagh invited him to join the newly-formed Renaissance Theatre Company as actor, composer and musical director. Doyle subsequently appeared in and wrote the incidental music for the company's productions, including "Hamlet", "As You Like It" and "King Lear".

Doyle segued to film composition with his award-winning score for Branagh's film adaptation of "Henry V" (1989). The music was both rousing and elegiac; the extended sequence of the dirge-like "Non nobis dominie", during which Henry carries the body of a fallen youth across the bloodied battlefield, was particularly noted by critics. Doyle subsequently fashioned the Bernard Herrmann-influenced music for Branagh's romantic thriller, "Dead Again" (1991), the sunny, soaring themes for "Much Ado About Nothing" (1993) and the sweeping, sometimes martial, score for "Hamlet" (1996).

Additionally, Doyle provided the lilting, Celtic-influenced score for "Into the West" (1992) and the strong, thrilling Hermannesque music for "Carlito's Way" (1993). His richly varied score for "A Little Princess" (1995), incorporating various influences (e.g., Indian, Victoriana), won acclaim (and a citation from the Los Angeles Film Critics) and was a brilliant compliment to the film's gorgeous visuals. Also in 1995, Doyle provided the charming, appropriately romantic, themes for Ang Lee's "Sense and Sensibility".