Mainieri is from New Jersey. He graduated from West Virginia University in 1963 with a Ph.D. in education and administration. He served as an assistant coach in college football at Columbia University under head coach Lou Little.
Mainieri served as the head coach at Miami Dade Community College for thirty years, starting in 1960. He was named athletic director in 1963. Mainieri became the first junior college coach to win 1,000 career games. Mainieri won 1,012 games at Miami-Dade.
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