He played for the Los Angeles Dodgers and Minnesota Twins between 1977 and 1985. He was in the bullpen for the Dodgers in the 1981 World Series, pitching one inning against the New York Yankees. He also pitched one season in Japan for the Chunichi Dragons in 1987.
Castillo is credited with teaching his former Dodgers team-mate, Fernando Valenzuela, how to throw a screwball.
Castillo died on June 30, 2014 from cancer at the age of 59.