Dillon began acting in both television and films in the 1980s. In 1983, Dillon played Arnold Norberry in the television film "No Big Deal". His first major role was Ed Rooney in the film "Heaven Help Us", directed by Michael Dinner. He received wide attention for his role as the psychopathic soldier Bunny in the 1986 film "Platoon." In 1988, he portrayed Brian Flagg in a remake of the 1958 American science fiction film "The Blob". It received mixed reviews but was praised for its special effects and has since gained a cult following. Other notable film roles from that period included "War Party" (1988), "No Escape" (1994), and "The Doors" (1991), in which he played drummer John Densmore.