2010-11:Anthony Mantha made his QMJHL debut, appearing in two games with Val-d'or, spending most of the season with the College Charles-Lemoy Riverains in Quebec's midget AAA league. Selected by the Foreurs in the fifth round (76th overall) of the 2011 QMJHL Entry Draft, he played in two December games for Val-d'or, with no points and a minus-two plus/minus. He was the third-leading scorer for the Riverains, scoring 20 goals with 24 assists in 37 games, and had 42 penalty minutes. In five playoff games he scored 2 goals with 3 assists and had 2 penalty minutes.
2011-12: Mantha played in 63 games for Val-d'or in his first full year in the QMJHL and represented Canada in the 2012 U18 World Junior Championship. He scored 22 goals with 29 assists and was minus-11 with 39 penalty minutes. The Foreurs were second in the West Division. Mantha scored 2 goals with 2 assists and was minus-nine with 6 penalty minutes in the wild four game playoff series with Rimouski. He joined Canada after the Val-d'or was eliminated and in seven games at the U18 WJC he scored 1 goal and was minus-two.
2012-13: Mantha was Val-d'or's second leading scorer behind Penguins prospect Anton Zlobin in his second season. He led the QMJHL with 50 goals and had 39 assists in 67 games and was plus-21 with 71 penalty minutes. The Foreurs reached the second round in the playoffs after finishing fourth in the West Division. Mantha scored 5 goals with 7 assists and was plus-1 with 13 penalty minutes in nine playoff games. He was ranked 10th amongst North American skaters in Central Scouting's mid-season rankings prior to the 2013 NHL Draft, and remained in that position in the CSS final rankings.