As a kid growing up in Toronto, Tom McCarthy was a scoring star playing in the elite MTHL. While playing for the North York Rangers Tier Two Junior A team in 1976-77 he had 49 goals and 96 points in 43 games while leading them to the Ontario championship. He also played his first two major junior games that year as an underaged player with the Kingston Canadians, scoring once.
Thanks to his stellar minor-league statistics, McCarthy was selected first overall in the junior draft, and the pressure that followed was incredible. In fact, when McCarthy first arrived in Oshawa he was greeted by a chorus of boos from the Generals fans. It was not so much a personal attack on McCarthy as it was the fans' verbal disapproval that team bypassed another young phenom by the name of Wayne Gretzky, who wound up going to Sault Ste. Marie. "I feel it everywhere I go," McCarthy said at the time. "Even at school people talked about it." Nonetheless, McCarthy soon gained the approval of the local fans with his own brand of excellent play. In 1977-78 McCarthy continued the torrid scoring pace he had enjoyed in the MTHL with the Generals, netting 43 goals and 93 points in 62 games to lead the team. He had such as good season that he was offered a lucrative contract by John Bassett to become one of the underage players on the WHA's Birmingham Bulls in 1978-79, but on the advice of his grandfather and agent Graham Stewart, felt he was not mentally prepared to turn professional and instead decided to return for a second season with the Generals while enrolling in Durham College where he studied sports administration. As good as his rookie season had been, McCarthy put up incredible numbers that year, drawing huge national attention scoring 69 goals and 144 points.
McCarthy was selected in the first round, tenth overall in the 1979 NHL Entry Draft by the Minnesota North Stars. General Manager Lou Nanne had his eye on McCarthy for most of the season and was amazed he was still available with the tenth pick. As a 19-year-old, with still a year of junior eligibility remaining, McCarthy was able to crack the Stars' starting lineup and in 68 games he responded with 16 goals and 36 points. At the start of the year McCarthy was quoted as saying "The decision to pass up the last year of junior was entirely up to me. I didn't have a clue what my chances would be of making the North Stars and I didn't know what to expect."
McCarthy's NHL career seemed like it was well under way after a successful rookie campaign. He remained with the team for five years and in his second season helped the club reach the Stanley Cup finals, where they were defeated by the New York Islanders. After playing 25 games in 1985-86 McCarthy was stricken by Bells Palsy and was forced to miss the rest of the season. The North Stars may have felt his career was over and traded him in May 1986 to the Boston Bruins for a third-round pick in 1986 and a second-round pick in 1987 which turned out to be Rob Zettler and Scott McGrady, respectively. McCarthy returned to hockey and played one full season with the Bruins, scoring 30 goals and 59 points in 68 games. He was back with the team for another seven games the following year. He played his last pro hockey season in Italy in 1988-89 with HC Asiago.