Marinelli joined the Chicago Bears in January 2009 as assistant head coach and defensive line coach, reuniting him with Lovie Smith, whom he worked with under Tony Dungy in Tampa Bay from 1996–2000. Marinelli also interviewed with the Houston Texans and Seattle Seahawks before joining the Bears. Marinelli was promoted from defensive line coach to defensive coordinator in February 2010. In the 2010 to 2012 seasons, Marinelli's defenses ranked ninth, seventeenth, and fifth, respectively. Also in 2012, the Bears led the NFL in interceptions with 24, along with in takeaways with 44, sixth in third-down efficiency (35.5 percent) and eighth in sacks with 41, while ranking third with the fewest points allowed (477). Marinelli left the Bears in January 2013.