Before becoming a coach, Mayo was an NFL linebacker and spent his entire playing career on the Patriots. He was their first round draft pick in 2008 and stayed there until retiring after the 2015 season.
Mayo finished his playing career as a Defensive Rookie of the Year, a Super Bowl champion, a 2-time Pro Bowler, and a First-Team All-Pro.
Just a few years after retiring from the NFL, Mayo returned back to New England as a coach. He was hired by the team as an inside linebackers coach in 2019, and stayed at that position until being promoted as the head coach.