Dave Gagner came up through the Chatham minor hockey system before joining the Brantford Alexanders for two full seasons. In 1982-83 he had a great offensive season, scoring 55 goals and 121 points in 70 games.
That summer Gagner was selected by the New York Rangers in the first round, 12th overall in the NHL Entry Draft. In 1983-84 he devoted himself to playing for the Canadian National Team, suiting up for 50 games and also playing in the 1984 World Championships. Gagner then lived out a dream by playing for Canada at the 1984 Olympics in Sarajevo, and although the team failed to medal, he always regarded it as one of the main highlights of his hockey career.
In 1984-85 Gagner began his pro career playing 38 games with the New York Rangers, scoring six goals and 12 points. He remained with the Rangers' organization for another two years but never was able to completely get over the hump and earn a full-time roster spot. The bigger, stronger players in the NHL posed a noticeable problem for players such as Gagner, who relied on speed to combat a lack of size. But in the NHL most players had both size and speed.
Gagner was traded to the Minnesota North Stars in October, 1987 hoping to revitalize his sagging career. He seemed to like the Stars offensive system much more and managed to surpass the 30-goal plateau in each of the five full seasons he was with the team. He also had two 40-goal seasons with his best year coming in 1990-91 when he had 40 goals and 82 points. That was also the year the North Stars advanced to the Stanley Cup finals, where they lost to Mario Lemieux and the Pittsburgh Penguins. Gagner was an offensive juggernaut throughout the playoffs for Minnesota, collecting 27 points in 23 games.
Gagner remained with the North Stars in Minnesota until the club moved to Dallas and he remained with the team for three more years in Texas. Midway through the 1995-96 campaign he was traded to the Toronto Maple Leafs, but he was there for just 28 games before they shipped him off to Calgary. He played the entire 1996-97 season with the Flames and had a solid 60-point season
In the summer of 1997, Gagner signed a free-agent pact with the Florida Panthers where he played for a little over a year before being traded to the Vancouver Canucks midway through the 1998-99 season. He finished out the year and then announced his retirement after 15 years in the NHL