2009-10: Drafted by the Kitchener Rangers in the 8th round (143rd overall) in the 2009 OHL Priority Draft, Thomson skated in 46 games for Kitchener in his first season and represented Ontario in the 2010 U17 World Hockey Challenge. He scored 6 goals with 6 assists and was plus-2 with 30 penalty minutes. Kitchener finished second in the Midwest Division and reached the playoff semifinals. Thomson skated in 11 of 20 playoff games and was an even plus/minus with 1 assist and 6 penalty minutes. In six games for silver medal-winning Canada Ontario at the U17 WHC he scored 1 goal with 1 assist and had 2 penalty minutes.
2010-11: Thomson provided a physical presence to a Kitchener lineup with several high profile offensive prospects in his second season with the Rangers. One of three players to play in all 68 games, he had the third-most penalty minutes (107) for Kitchener and scored 6 goals with 13 assists ; finishing minus-seven. Kitchener again finished second in the Midwest Division and fell to Plymouth in a first round playoff series. Thomson skated in all seven games and had 1 assist with 6 penalty minutes. He was ranked 146th amongst North American skaters in Central Scouting's final rankings prior to the 2011 NHL Draft but was not selected in his first year of eligibility.
2011-12: Thomson displayed some play-making ability to go along with his physical presence and had the Rangers' third-best plus/minus (plus-21) in his third OHL season with Kitchener. In 67 games he scored 11 goals with 30 assists and was second on the team with 137 penalty minutes. Kitchener reached the playoff semifinals after finishing second to OHL champion London in the Midwest Division. In 16 playoff games Thomson scored 5 goals with 5 assists and was minus-five with 36 penalty minutes. Not among the 210 North American skaters in Central Scouting's final rankings, Thomson was selected by New Jersey in the fourth round (96th overall) of the 2012 NHL Draft.
Thomson's bread and butter is his size and physicality. That makes him very effective along the boards and in the corners as he is nearly impossible to knock off the puck when he is in on the cycle. Despite a minor-breakthrough offensively in 2011-12, he's never going to be confused as a player with a lot of natural puck skills and creativity. He does skate well for his size, is responsible defensively and will not hesitate to drop the gloves when the time calls for it.
Thomson has traits in his repertoire that could eventually see him develop into an effective fourth-line energy guy in the future, but he’s going to have his work cut out for him to make it at the professional level. He’ll return to the Kitchener Rangers this fall for another season of junior.