Keon joined the Toronto Maple Leafs of the National Hockey League for the 1960–61 season, winning the Calder Memorial Trophy as the league's top rookie with 20 goals and 45 points in his first season. It was his first of six consecutive 20-goal seasons. In his second year in the NHL, Keon was named to the Second All-Star Team and won the Lady Byng Memorial Trophy as most gentlemanly player, taking only one minor penalty through the entire season. He repeated as Lady Byng winner in 1962–63, again taking only a single minor penalty all year.