Pearn, a three-time national kart racing champion in Canada, competed in late models. In 2001, Pearn debuted in the CASCAR Super Series at Delaware Speedway, finishing 17th. Pearn competed full-time in 2002 and 2003, driving the No. 24 Pontiac and recording a best finish of sixth twice: in 2002 at Delaware and 2003 at Race City Speedway.
After graduating from college, Pearn worked for Toyota, and later moved to North Carolina. He joined Richard Childress Racing in 2007, working with Kevin Harvick's No. 29 crew as an engineer. In 2010, he joined Furniture Row Racing as a team engineer, though he left for JTG Daugherty Racing in 2011. Pearn returned to FRR during the 2012 season, becoming the team's lead race engineer. On December 3, 2014, Pearn was promoted to crew chief of the No. 78, replacing Todd Berrier, who had departed the team to join Joe Gibbs Racing, and Pearn became the first regular Canadian crew chief in Cup Series history. In 2015, Pearn and driver Martin Truex Jr. won the Axalta "We Paint Winners" 400 at Pocono Raceway, and Pearn became the first Canadian crew chief to win a Cup race. In 2016, Pearn was suspended for the Kobalt 400 after failing technical inspection at the Folds of Honor QuikTrip 500; the team had also been penalized at the Daytona 500 the week before for roof flap problems. During the 2017 season, Pearn and Truex won eight races en route to the series championship.