The son of immigrants from Croatia, Mahovlich was scouted by several National Hockey League teams while playing for the Schumacher Lions of the Northern Ontario Hockey Association. He signed with the Toronto Maple Leafs, who sent him to one of their Ontario Hockey Association affiliates, the Toronto St. Michael's Majors. Mahovlich played there while attending St. Michael's College School from 1954 to 1957. While at St. Michael's, he received instruction from Joe Primeau, who Mahovlich would later call the best coach he ever had. Mahovlich received the Red Tilson Trophy as the top player in the OHA for the 1956–57 season, in which he scored 52 goals in 49 games.