Gartner was drafted in the 1st Round, 4th overall by the Washington Capitals in the 1979 NHL Entry Draft. Mike Gartner started his professional career playing in the WHA as an underager with the Cincinnati Stingers in 1978-79. He played on a line with Mark Messier and had a successful campaign, finishing second to Wayne Gretzky for Rookie-of-the-Year honors. As a result, he With the WHA folding at the end of the season, he played the next season with the Capitals, and would play for them for the better part of ten seasons. He recorded an assist in his NHL debut on October 11, 1979 versus the Buffalo Sabres, and he wore number eleven for the Caps.

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. He also led the team with 36 goals. Gartner was traded to the Minnesota North Stars on March 7, 1989 with Larry Murphy for Dino Ciccarelli and Bob Rouse. He left the Capitals as the team's all-time leader in career goals, assists and points, and currently stands second in those three categories.

However, Gartner only lasted one season with Minnesota and was traded to the New York Rangers on March 6, 1990 for Ulf Dahlen, a draft pick and future considerations. He had a strong start with the Rangers scoring two goals in his debut versus the Philadelphia Flyers. In fact, he scored eleven goals and sixteen points in the remaining twelve regular season games the Rangers played that year. In 1991-92, he became the first player in NHL history to score his 500th goal, 500th assist, and 1000th point all in the same season. The next season, Gartner became the first Ranger to score at least 40 goals in three consecutive seasons. He also scored four goals in the NHL All-Star Game and earned the All-Star Game MVP award.

In 1993-94, Gartner was traded to the Toronto Maple Leafs for Glenn Anderson, a minor leaguer and a draft pick. He played with the Leafs until 1996, when he was traded to the Phoenix Coyotes, who had just re-located from Winnipeg. Gartner scored the first goal and hat trick in Phoenix history on October 7 against the Boston Bruins, in the franchise's second game. He played two seasons with the Coyotes before retiring in August, 1998.

Despite his impressive career, Gartner never won the Stanley Cup or played in the Finals. Only Phil Housley has played in more games (1432) without winning the Cup. He was a member of the New York Rangers team that would go on to win the championship in 1994, but he was traded to Toronto before the deadline. He was traded close to the NHL Trading Deadline three times in his career, and had a knack for producing immediately for those teams, as in a combined 35 games with his new teams during the regular season after the mid-season deals, he had 24 goals, 18 assists, 42 points, and a +16 rating.

Gartner himself was noted for his consistency in his career, as evidenced by his NHL-record 14-consecutive 30+ goal seasons. He lead his team in goals nine times during his career. He also did not miss a game in eight of his nineteen NHL seasons. Gartner became only the fifth player in NHL history to reach at least 700 goals, despite never scoring more than 50 in a single season. Since his totals were strong but never close to the scoring leaders, this explained why Gartner never made the First Team All-Star or Second Team All-Star, nor won a major NHL award.

Gartner is also active with the NHL Players Association. He served as president of the NHLPA from 1996 until his retirement in 1998 and currently serves as Chairman of the Goals & Dreams program with the NHLPA

Gartner is a Born-again Christian, and was introduced to the faith during his playing days by former Washington teammate Jean Pronovost. His son, Josh, played goalie for Yale University.

Michael Alfred Gartner was inducted into the Hockey Hall of Fame in 2001. He is the first inductee to have never: win the Stanley Cup, play in the Cup finals, win an NHL award, and be named to the postseason All-Star Team.