Gartner had a solid season in 1979–80, winning the Capitals' Rookie of the Year and MVP awards, as well as being voted by their fans as the team's Most Promising Player.

Gartner was traded to the Minnesota North Stars on March 7, 1989, with Larry Murphy for Dino Ciccarelli and Bob Rouse.

[2] However, Gartner only lasted one season with Minnesota and was traded to the New York Rangers on March 6, 1990, for Ulf Dahlén, a draft pick and future considerations.

He scored eleven goals and sixteen points in the remaining twelve regular-season games the Rangers played that year.

[3] The deal was driven by Rangers head coach Mike Keenan who disliked Gartner for his lack of grit and disappointing performances in the playoffs.

Rangers general manager Neil Smith convinced his Maple Leafs counterpart Cliff Fletcher to agree to the trade by noting that Gartner had one year left on his contract while Anderson was expected to become a free agent at season's end.

Gartner scored the first goal and hat trick in Phoenix history on October 7 against the Boston Bruins, in the franchise's second game since relocation.

However, Gartner got farther than he ever would in the playoffs that same year, as the Maple Leafs made it to the Western Conference Finals before losing to the Vancouver Canucks in 5 games.

[10] During the 1996 Super Skills competition, Gartner had set the record for the fastest skater event with a time of 13.386 (Full course standing start).

His son, Josh, played goalie for Yale University and right wing for the Tuck School of Business A-Team in the Upper Valley Hockey League.