He was also a member of the Ohio Bobcats track and field team, where he was a premiere sprinter and placed sixth in the 100 meter dash at the 2004 Mid-American Conference championships.

Cox was originally signed by the Detroit Lions as an undrafted rookie free agent on April 28, 2005, and he spent the 2005 training camp and preseason with the team.

After switching to the linebacker position for the 2009 season, Cox led the CFL in forced fumbles and capped off the year by winning the 97th Grey Cup with the Alouettes.

He also had 12 sacks (career high) and four interceptions en route to winning the CFL's Most Outstanding Defensive Player Award and the James P. McCaffrey Trophy.

On December 2, 2014, the Alouettes announced that they had resigned Cox to a three-year deal worth more than $200,000 annually, which general manager Jim Popp stated would make him the CFL's highest-paid defensive player.