Jim Conacher and his family moved from Scotland to Canada when he was six. Growing up in and around the Toronto area, he played in the local outdoor league until being picked by the OHA's Oshawa Generals in 1940. Nicknamed "Pencil" because of his lightweight, he began his professional career in 1941 with the Omaha Knights of the AHA, a farm team of the NHL's Detroit Red Wings. In 47 games, he scored 44 points and the club went on to win the playoff championship. His professional career was put on hold for three years during World War II. When he returned in 1945-46, Conacher played 20 games for the Detroit Red Wings, scoring a goal and six points. The rest of the season he played in the AHL with the Indianapolis Capitals where he had 47 points in just 32 games.
In 1946-47, Conacher played 33 games with the Red Wings, notching 16 goals and 29 points in 33 games. The following year he had 40 points while suiting up for 60 games. The Red Wings advanced to the Stanley Cup finals, where they lost in four-straight games to the Toronto Maple Leafs.
Conacher began the 1948-49 season in Detroit, but after just four games was traded to the Chicago Blackhawks, which came as a welcome move for Conacher, who always had expressed a desire to play in the Windy City. Although not a member of the famed Conacher family that included Lionel, Ray, and Hawks' manager, Charlie, Jim Conacher once scored four goals in a game for Chicago, which prompted Charlie Conacher to joke that "maybe we ought to adopt him into the family." That week he was named the NHL player of the week, earning two free hats for his honour. In his first year with Chicago, Conacher scored a career-high 25 goals and 48 points in 55 games.
In 1949-50, Conacher dressed for 66 games, scoring 13 goals and 33 points. He played another full season in Chicago before being sent to the New York Rangers in 1951-52 where he played out his NHL career, retiring after dressing for 17 games in the 1952-53 season.