Marinelli began as an undergraduate at Utah in 1968, where he played offensive and defensive tackle. After military service in Vietnam, he attended Cal Lutheran with a physical education major, and was a member of Bob Shoup's legendary 1971 NAIA National Championship team on which  he was team captain and National Association of Intercollegiate Athletes (NAIA) All-America offensive tackle.

Rod has been in coaching for forty years. Here is a brief breakdown on his coaching experience:

• 1973-75, Rosemead High School (assistant coach);
• 1976-82, Utah State (defensive line/offensive line/special teams coach);
• 1983-91, California (assistant head coach/defensive line coach);
• 1992-93, Arizona State (assistant head coach/defensive line coach);
• 1995, USC (defensive line coach);
• 1996-2005, Tampa Bay Buccaneers (defensive line coach/assistant head coach);
• 2006-08, Detroit Lions (head coach).
• Named Chicago Bears defensive line coach and assistant head coach in January 2009.
• Named Dallas Cowboys defensive line coach in January 2013.

When Marinelli talks about life in the National Football League, he points to the difference fundamentals, discipline, work ethic, attention to detail, leadership, passion and commitment truly make. Dallas’ new Defensive Line Coach, who coached at the high school and university levels before moving to the NFL, also talks about wanting a roster made up of players who have true "football character" — players who have such a profound love of football that they will not allow anything to compromise or interfere with their desire and preparation to be the very best they can be.

Rod is a specialist with the 4-3 defense, and his statistics show it. During Marinelli's time in Tampa, which covered a span of 10 seasons, the Buccaneers had more sacks than any other franchise in the NFL. In his three years in the Windy City, the Bears have twice ranked in the top 10 in total defense. In all three of his seasons as the defensive coordinator, the Bears finished in the top five in defensive takeaways and had 44 in 2012 as opposed to the Cowboys' 16.