Before turning pro, Pearson played two seasons with Barrie of the Ontario Hockey League beginning in 2010-11. He was the OHL's third-leading scorer in 2011-12 with 91 points (37 goals). Pearson also scored one goal and six points in six games to help Canada finish third at the 2012 IIHF World Junior Championship.
In an unexpected move, Pearson became the third player in Los Angeles Kings history to make his NHL debut in the Stanley Cup Playoffs. Twice passed over in the NHL Draft, Pearson was selected by the Kings in the first round (No. 30) of the 2012 NHL Draft, less than two months before his 20th birthday. A gifted left wing with a strong shot, Pearson was called up by the Kings after playing the 2012-13 season for Manchester of the American Hockey League. The Kitchener, Ontario, native was in the lineup for Game 3 of the Western Conference Semifinals against the San Jose Sharks on May 18, 2013.