He attended Monterey High School (1958–1962) where he was an all conference baseball and football player and starter on the varsity basketball team.

Colletto was the offensive coordinator for the Detroit Lions of the National Football League, replacing Mike Martz, who was fired on January 2, 2008.

Colletto was named Purdue University's head coach in December 1990, accepting the position while he was serving as the offensive coordinator for Ohio State.

[1] During his introduction press conference, he stated that at the practice field, he planned to install a small cemetery in which he would place a tombstone for every school Purdue upset or beat on the road.

[9] Colletto was subsequently defeated his first year as OC at Notre Dame at the hands of the Purdue Boilermakers.