After landing a role in the 1990 horror film Clownhouse, Rockwell began studying at the William Esper Studio in New York. Small parts in TV shows and independent films followed, and in 1996, he caught the attention of critics with his portrayal of an off-kilter loner opposite John Turturro in Box of Moonlight.
After a decade of roles in small films, Rockwell finally found mainstream success playing killer "Wild Bill" Wharton in The Green Mile (1999). Since then, he's continued to move with ease between both worlds, providing memorable performances in such films as Confessions of a Dangerous Mind, Matchstick Men and Joshua.