He played college football for the Mississippi State Bulldogs, and was selected by the Eagles in the first round of the 2012 NFL draft.

He chose to attend Mississippi State over scholarship offers from LSU, Alabama, Auburn and Ole Miss.

[12] During his rookie year in 2012, Cox played 15 games and finished with 39 tackles, 5.5 sacks, four passes defended, and one forced fumble.

[15] In the 2014 regular season opener for the Eagles, Cox had a 17-yard defensive fumble return for a touchdown in the 34–17 victory over the Jacksonville Jaguars.

[17] His presence along the Eagles defensive line led to league-wide recognition and Second-team All-Pro honors.

[20] For his game against the Saints, he earned National Football Conference (NFC) Defensive Player of the Week.

[22] For his efforts, Cox received Second-team All-Pro honors and was selected to the Pro Bowl for the first time in his career.

[31] On September 10, 2017, in the season opening 30–17 victory over the Redskins, Cox recovered a fumble from quarterback Kirk Cousins and returned it for a touchdown late in the fourth quarter to help put the game away.

[39] In addition to being named to his fourth Pro Bowl, he was selected as a first team All-Pro for the first time in his career.

[42] In Week 7 against the Dallas Cowboys, Cox recorded his first sack and forced fumble of the season on Dak Prescott in the 37–10 loss.

[46][47] Following the season, Cox was selected as one of the four defensive tackles on the National Football League 2010s All-Decade Team.

[52] In Week 15, Cox recorded two sacks and four quarterback hits against the NFC East rival Washington Football Team.

[56] On March 17, 2022, Cox was released by the Eagles at the start of the new league year,[57] but was re-signed two days later on a one-year contract.