Reilly made his film debut in the Brian De Palma war film Casualties of War as PFC Herbert Hatcher in 1989. Although his role was written as a small one, De Palma liked Reilly's performance so much that the role was significantly expanded. He played Buck, Tom Cruise's character's NASCAR car chief in Tony Scott's Days of Thunder in June 1990. That September, he played an Irish hoodlum named Stevie McGuire in the crime film State of Grace, which starred Sean Penn; Reilly had previously appeared as a monk in the comedy We're No Angels (1989), which also starred Penn. In 1992's Hoffa, Reilly played Jimmy Hoffa's (Jack Nicholson) associate who testifies against him at Hoffa's trial. Reilly appeared in a supporting role in What's Eating Gilbert Grape (1993), playing one of the titular character's (played by Johnny Depp) friends. His next role was in The River Wild (1994), in which Reilly appeared alongside Kevin Bacon as a pair of criminals who terrorise a family during a rafting trip. In 1995, Reilly appeared in the psychological thriller Dolores Claiborne as a police constable and in the drama Georgia as a drug-addict drummer in the band Jennifer Jason Leigh's character joins.