Following a season in the MCHL with Montreal, controversy arose as to who owned Gallagher's NHL playing rights. Toronto had signed him to a free-agent contract, but it was ruled he was the property of the Montreal Maroons. He played two full seasons with the Maroons before being dealt to the Detroit Red Wings early in the 1932-33 campaign.

Gallagher missed the majority of the 1933-34 season, recovering from serious injuries sustained in an automobile accident. He was briefly sent to the New York Americans in a trade hut was soon dealt back to the Red Wings. He was then sent back to New York for a second time which is where he played out his days as an NHL defenseman.

In 205 NHL games, Gallagher netted 14 goals and 33 points.

Courtesy of the Hockey Hall of Fame