McClellin recorded a sack and forced a fumble against Hawaii, as well as blocking a field goal attempt against Oregon.

[6] In McClellin's junior year, he recorded 30 tackles on the season, including 13.5 tackles-for-loss – tied for the most on the team – and a team-high 9.5 sacks.

He tied his career high with six tackles against Virginia Tech in the team's 2010 season opener.

McClellin also forced one fumble and recovered two, one of which was returned for a touchdown against Wyoming, and returned an interception 36 yards for a touchdown against the Toledo Rockets, becoming the first Bronco defensive player to score on a fumble recovery and an interception in the same season since 1999.

Boise State would ultimately go to the 2010 Maaco Bowl Las Vegas, and triumph over the Utah Utes.

In his final game of his college career, McClellin recorded 3 tackles for losses in the victory against the Arizona State Sun Devils in the 2011 Maaco Bowl Las Vegas.

[14] Chicago Bears general manager Phil Emery stated that he intended on drafting McClellin as an outside linebacker during his time with the Kansas City Chiefs.

[15] McClellin later worked out for 11 teams, including the Patriots, Chiefs, Buffalo Bills, Tennessee Titans, Indianapolis Colts and the Cleveland Browns.

Analysts believed that he could go to the Bears, Packers, San Diego Chargers, Baltimore Ravens, Houston Texans, Pittsburgh Steelers or the New York Jets.

"After getting drafted by Chicago, Emery stated that McClellin would play opposite Julius Peppers at left defensive end,[20] with Chicago Sun-Times writer Sean Jensen saying that McClellin could replace middle-linebacker Brian Urlacher in the event that he leaves the team or retires.

[22] McClellin made his NFL debut in week one of the preseason against the Denver Broncos, recording three tackles, one sack (on former Bear Caleb Hanie), one tackle-for-loss, and two quarterback hits.

McClellin was penalized for a helmet-to-helmet hit on Hanie, setting up a Broncos field goal; even though the kick missed, the Bears would lose 31-3.

[35] On February 5, 2017, McClellin started at linebacker in the Patriots' Super Bowl LI 34–28 overtime victory over the Atlanta Falcons.

[40] In 2012, McClellin became a partner with Allstate and Give Your Sole, and attended the Chicago 13.1 Marathon on June 9 to encourage runners to donate athletic shoes.

On June 8, McClellin and the rest of the 2012 Bears draft class planted trees and shrubs at LaFollette Park as part of the team's Save Da Planet program.