He played college football for the Purdue Boilermakers, earning unanimous All-American honors as a senior before being selected by the Washington Redskins in the first round of the 2011 NFL draft.

A three-star recruit, Kerrigan committed to Purdue over offers from Ball State, Cincinnati, Indiana, and Northern Illinois.

As a sophomore in 2008 he started 11 of 12 games and was an honorable mention All-Big Ten selection after recording 56 tackles, seven sacks and an interception.

[2] Following his 2010 season, he was recognized as a unanimous All-American, honored as the Big Ten Defensive Player of the Year, and won the Bill Willis Trophy.

[6][7] Kerrigan made his professional regular season and first career start in the Redskins' season-opener against the New York Giants and recorded five combined tackles, a pass deflection, and returned an interception for a touchdown in their 28–14 victory.

Kerrigan intercepted a pass by quarterback Eli Manning, that was originally intended for wide receiver Hakeem Nicks, and scored a nine-yard touchdown in the third quarter.

[11] On November 13, 2011, Kerrigan collected a season-high six combined tackles and had two sacks on quarterback Matt Moore during a 20–9 loss at the Miami Dolphins.

[13] On October 7, 2012, Kerrigan recorded five combined tackles, deflected a pass, and returned an interception for a touchdown during a 24–17 loss to the Atlanta Falcons in Week 5.

[17] Kerrigan started all 16 games in 2012 and recorded 54 combined tackles (42 solo), 8.5 sacks, eight pass deflections, an interception, and a touchdown.

[18] Defensive coordinator Jim Haslett retained Kerrigan, Brian Orakpo, Perry Riley, and London Fletcher as the linebacking corps in 2013.

[19] He started in the Washington Redskins' season-opener against the Philadelphia Eagles and collected a season-high eight combined tackles and made one sack in their 33–27 loss.

[24] On September 19, 2014, Kerrigan recorded four solo tackles and had a career-high four sacks on quarterback Chad Henne during the Redskins' 41–10 victory against the Jacksonville Jaguars in Week 2.

He started in all 16 games in 2014 and recorded 64 combined tackles (51 solo), a career-high 13.5 sacks, five forced fumbles, and a pass deflection.

[27] On December 31, 2014, the Washington Redskins announced the decision to mutually part ways with defensive coordinator Jim Haslett.

Kerrigan started in all 16 games for the fifth consecutive season and recorded 42 combined tackles (33 solo), 9.5 sacks, three pass deflections, and two forced fumbles.

On January 10, 2016, he made two combined tackles and a pass deflection during the Redskins' 35–18 loss to the Green Bay Packers in the NFC Wildcard Game.

[40] He started in the Washington Redskins' season-opener against the Philadelphia Eagles and recorded three combined tackles, half a sack, a pass deflection, and returned an interception for a touchdown during a 30–17 loss.

Kerrigan intercepted a pass by quarterback Carson Wentz, that was initially intended for running back Darren Sproles, and returned it for a 24-yard touchdown in the second quarter.

[41] In Week 7, he collected a season-high six combined tackles and was credited with half a sack as the Redskins lost at the Philadelphia Eagles 34–24.

[43] In 2018, Kerrigan stripped the ball from quarterback Dak Prescott in the end zone, which was recovered by Preston Smith and scoring a defensive touchdown that helped seal the Week 7 win against the Dallas Cowboys.

[48] In Week 12 against the Detroit Lions, Kerrigan recorded half a sack on Jeff Driskel before exiting the game with a concussion.