Hackett began his coaching career at his alma mater, UC Davis, in 1969, assisting the freshmen in the first year and then directing them to a 13-0 mark over the next two seasons under College Football Hall of Fame coach Jim Sochor. He then was an assistant at California for four years (1972–75), the first season as a graduate assistant, the next as the receivers coach and the final two as the quarterbacks coach. Then, at age 29, he moved to USC for five years (1976–80) as an assistant coach under John Robinson; Hackett would succeed Robinson at USC after the latter's second tenure as head coach.