In 1950, Lewicki began his National Hockey League career with the Maple Leafs. As a nineteen-year-old, he made the team straight out of training camp. Lewicki was able to get a one-way contract at $10,000 for three years and a signing bonus of $3,000. Lewicki made his NHL debut on October 14, 1950 against the Chicago Black Hawks. In his seventh game, Lewicki scored his first NHL goal on a bounce off the glass that bounced off the back of the Boston Bruins Jack Gelineau. Lewicki became a contender for the Calder Trophy, although he had strong competition from future Hall of Famer Terry Sawchuk. Lewicki had 16 goals and 31 assists before a groin injury ended his season early. Lewicki would end up third in voting for the Calder. The team finished second to qualify for the playoffs. Lewicki was pressed into service on the orders of Conn Smythe, although he was not healed. To play he had to have his groin muscle frozen and taped before each game. Instead of being able to contribute as a scorer, Lewicki would play a checking role in the playoffs. The Leafs would defeat the Montreal Canadiens in the final 4–1 to win the 1951 Stanley Cup Final. Lewicki was an Allan Cup, Memorial Cup and Stanley Cup winner at the age of 20.