2010-11: Jake Marchment appeared in three junior A games as a 15-year-old — scoring 1 goal with 2 penalty minutes for the Cobourg Cougars — and played for the Clarington Toros minor midget AAA team in Ontario. In 36 games for the Toros he scored 18 goals with 14 assists and 22 penalty minutes. Marchment was selected by Brampton in the sixth round (106th overall) in the 2011 OHL Priority Draft.
2011-12: Marchment skated for the Clarington Toros U18 midget team. In 26 games he scored 8 goals with 12 assists and 12 penalty minutes.
2012-13: Marchment played for the Wellington Dukes in the Ontario Junior Hockey League. He scored 7 goals with 13 assists and 50 penalty minutes in 49 regular season games. Wellington finished fourth in the East Division and lost to the Kingston Voyageurs in the first round of the playoffs. Marchment scored 1 goal with 1 assist and 7 penalty minutes in five playoff games. In January he committed to playing college hockey at Canisius College in 2013-14.
2013-14: Obtained by the Belleville Bulls from North Bay in an August trade, Marchment decided to pursue a junior career instead of playing college hockey. He appeared in 57 games for Bellevville as an OHL rookie. Marchment scored 10 goals with 22 assists and was +4 with 53 penalty minutes for the Bulls. Belleville missed the OHL playoffs; finishing fourth in the East Division. Not among the 210 North American skaters in the Central Scouting final rankings, Marchment was selected by Los Angeles in the sixth round (157th overall) of the 2014 NHL Draft.