Cox was signed by the Baltimore Ravens as an undrafted free agent following the 2010 NFL draft on May 6, 2010.[7][8] He earned the starting long snapper job after the Ravens released Matt Katula on August 14, 2010.[5] Cox was part of the 2012 Baltimore Ravens Super Bowl XLVII victory over the San Francisco 49ers on February 3, 2013.[9][10] In the season opener of the 2013 season against the Denver Broncos, Cox recovered a punt that was muffed by Wes Welker.[11] On October 19, 2014, Cox tore his ACL against the Atlanta Falcons and was placed on season ending injured reserve the day after.[12] He was replaced by Kevin McDermott for the remainder of the season. Cox recovered from the injury, and resumed his long snapping duties for the 2015 season. Cox, along with punter Sam Koch.[13]
On March 7, 2016, Cox signed a five-year contract extension with the Ravens.[14] He made the Pro Bowl for a second consecutive season for the 2016 season.[15] Cox made his third Pro Bowl for the 2019 season.[16]
In 2020, Cox was one of 18 players placed on the reserve/COVID-19 list before the Ravens' Week 12 game against the Pittsburgh Steelers. He was placed on the list on November 27, 2020,[17] and activated on December 7.[18] He was replaced by Nick Moore.[19] He earned his fourth Pro Bowl nomination.[20] He became the first long snapper to ever be selected to first-team All-Pro (this was the first year the NFL had long snappers on the ballot).[21] However, on January 25, 2021, the Ravens announced that they would be going with Nick Moore for the next season and would not be re-signing Cox.[22]
Tennessee Titans
On March 18, 2021, Cox signed a one-year contract with the Tennessee Titans.[23] He re-signed with the team on March 10, 2022.[24] He was named to the Pro Bowl for his 2022 season.[25]
On March 10, 2023, Cox re-signed on another one-year contract, and again on March 7, 2024.[26][27]