The Redskins made the pick Thursday night after moving down from the No. 10 spot in a trade with Jacksonville.
Kerrigan was a defensive end in college, but he will likely be used as an outside linebacker in Washington's 3-4 scheme.
The Redskins' defense ranked 31st in the league last year.
Washington moved down six spots in the deal with Jacksonville and also received the Jaguars' second-round selection, No. 49 overall.
The move was hardly a surprise. Coach Mike Shanahan had spoken about accumulating more draft picks. The Redskins have many holes to fill, and they began with draft without any selections in the third and fourth rounds.