Spent the first two years of his college career at Itawamba Community College in Fulton, Mississippi where he was named an NJCAA All-American as a sophomore, a season in which he led the nation with 13.5 sacks. During his career at ICC, he tallied 124 tackles, 32.5 sacks, 73.5 TFL, 47 QB pressures, and 4 FFs in 18 games.
After completing his two years at ICC he transferred to Mississippi State. He was named to the coaches All-SEC first-team as a senior in 2010 and was named first-team All-SEC as a junior in 2009. He served as a team captain in 2010. During his MSU career he started all 25 of the games in which he appeared and totaled 91 tackles, 7 sacks, 22 TFL, 20 QB pressures, 2 FFs, and 4 pass breakups. In 2009, he was twice named the SEC Defensive Lineman of the week.
Professional career
Baltimore Ravens
McPhee was drafted by the Baltimore Ravens in the fifth round with the 165th overall pick of the 2011 NFL Draft. McPhee collected 6.0 sacks as a rookie for the Ravens in 2011, plus 23 tackles and a forced fumble while playing in all 16 regular season games. On January 12, 2013, in the AFC Divisional Playoff against the Denver Broncos, McPhee recorded a strip-sack on quarterback Peyton Manning. The Ravens would go on win that game 38-35 in double overtime. On January 20, 2013, in the AFC Championship against the New England Patriots, McPhee tipped a pass from quarterback Tom Brady that led to an interception by Dannell Ellerbe with 6:49 remaining in regulation. This led to the Ravens winning that game 28-13 and earning a trip to Super Bowl XLVII, where they would defeat the San Francisco 49ers by a score of 34-31. McPhee switched from defensive end to outside linebacker for the 2013 season.
Chicago Bears
On March 10, 2015, McPhee signed a five-year contract with the Chicago Bears. On September 27on the road at CenturyLink Field, McPhee came up with two back to back sacks in a 26-0 loss to the Seattle Seahawks. In the 2015 season, McPhee led the team with 18 quarterback hits. McPhee started the 2016 season on the PUP list with a knee injury. He was activated to the active roster on October 20, 2016. In 2017, McPhee played in 13 games with five starts before suffering a shoulder injury in Week 15. He was placed on injured reserve on December 20, 2017. On February 26, 2018, McPhee was released.
Washington Redskins
On March 26, 2018 McPhee signed a one-year, $1.8 million contract with the Washington Redskins.
Baltimore Ravens (second stint)
On May 17, 2019, McPhee signed with the Baltimore Ravens. He was placed on injured reserve on October 21, 2019 with a triceps injury. On May 12, 2020, McPhee re-signed with the Ravens.