Mantha had 81 goals in 81 games and added another 77 assists for the Quebec Major Junior Hockey League champion Foreurs.
"For sure I'm proud of that," the towering winger said. "It's a lot of goals, but the credit needs to come back to my teammates that helped me out through this year.
"I think it was just a great season. I put a lot of pressure on myself by leading the team on the ice, off the ice also."
Mantha was chosen for the CHL's top individual trophy ahead of Western Hockey League nominee Sam Reinhart of the Kootenay Ice and the Ontario Hockey League's Connor Brown of the Erie Otters.
Brown was the CHL's top scorer in the regular season with 45 goals and 83 assists in 68 games. Reinhart earned the CHL's sportsmanlike award for recording just 11 minutes in penalties during the season.
Mantha accepted the top-player award not long after the Foreurs were eliminated from the MasterCard Memorial Cup. The Foreurs fell 4-3 in triple overtime to the Edmonton Oil Kings in Friday's semifinal.
The game was the longest game in Memorial Cup history at 102 minutes 42 seconds of play. Mantha's teammates had already departed for Val-d'Or on Saturday morning, but the right-winger remained in London to accept the player-of-the-year trophy.
"It does feel weird," Mantha acknowledged. "Today, it's an individual trophy that I won. For sure, I would have liked way better the trophy from (Sunday), but I mean I'll take this one.
"It's a trophy that my teammates helped me out to win this year and I need to give them the credit."
Mantha, six foot five and 204 pounds, finished the Memorial Cup with a goal and three assists. His was the lone goal in a 1-0 win over the host Knights to open the tournament.
Mantha was drafted in the first round and 20th overall by the Detroit Red Wings in the 2013 NHL entry draft. Foreurs coach Mario Durocher said during the Memorial Cup that Mantha returned from his first NHL training camp a changed player.
"Last year, I would say a lot of critics were on my consistency level," Mantha said. "When I went to Detroit they tried to put that mentality in me and I think it did work for this year. I came back with that attitude and it was just a great thing for me."
He was also Canada's top scorer at this year's world junior hockey championship with five goals and six assists in six games.
Previous winners of the CHL's top-player award include Jonathan Drouin (2013), Jordan Eberle (2011), John Tavares (2007), Sidney Crosby (2004, 2005), Brad Richards (2000), Eric Lindros (1991) and Joe Sakic (1988).
"It's a great award to win and I think it's something that's going to stay in mind for a few months if not for a few years, but I need to pass to another level in my career," Mantha said. "I think I'll be ready for it."
Derrick Pouliot of the Western Hockey League's Portland Winterhawks was named the CHL's top defenceman. The Pittsburgh Penguins prospect had 70 points in 58 games with a plus-minus of plus-40.
Jordan Cooke of the Kelowna Rockets earned the trophy for best goaltender. The 20-year-old posted a record of 39-7-0-4 with a goals-against average of 2.28 and a save percentage of .922,
Halifax Mooseheads forward Nikolaj Ehlers was chosen top rookie. The 18-year-old from Denmark had a plus-minus rating of plus-65 while contributing 49 goals and 53 assists in 63 games.
The coaching award went to Eric Veilleux of the Baie-Comeau Drakkar, who reached the QMJHL final before falling in seven games to Val-d'Or.
Kingston Frontenacs forward Sam Bennett was selected the top NHL prospect. He is ranked first overall among North American skaters by NHL Central Scouting for the draft next month.
Erie Otter forward Connor McDavid won the scholastic award with an 87 per cent average in his second semester of Grade 11.
Moose Jaw Warriors captain Sam Fioretti was recognized for his humanitarian work off the ice. He works with Moose Jaw police in their anti-bullying program.