He is six feet (183 cm) tall and, during his baseball career, weighed 175 pounds (79 kg). He played five seasons of baseball with the New York Mets of the National League from to . The Mets drafted him in the sixth round of the 1979 amateur draft. In his career, he played shortstop, second base, and third base. During his career, he was often plagued by injuries, especially to his hamstring muscle. Only twice in his career, in and , did he play over 70 games in the season.
For three years after he retired (1988-90), he was a manager in the Minnesota farm system, leading teams in the Class A Midwest League and Class AA Southern League to one second- and two first-place finishes. In , Gardenhire became the Twins' third base coach and held that post for 11 full seasons, including the team's 1991 World Series championship.
On January 4, , Gardenhire was named manager of the Twins, replacing Tom Kelly, who had won two World Series titles with the Twins. In contrast to "TK"'s relatively calm, Bud Grant-like coaching style, Gardenhire is a very active and aggressive manager, frequently exiting the dugout to argue with the umpire, leading some to joke that "Gardy" gets ejected more times in a season than TK did in his entire career (as of July 31, 2008, Gardenhire has been ejected 41 times). An early 2006 television commercial for the Twins pokes fun at this, showing Gardenhire arguing with a (presumably Twin Cities area) office worker planning to go home after work rather than go to the Twins game. He has been nicknamed 'Gardy'.
| Team | Year | Regular Season | Postseason | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Games | Won | Lost | Win % | Finish | Won | Lost | Win % | Result | ||
| Minnesota Twins | 2002 | 161 | 94 | 67 | .584 | 1st in American League Central | 4 | 6 | .400 | Lost in ALCS |
| 2003 | 162 | 90 | 72 | .556 | 1st in American League Central | 1 | 3 | .250 | Lost in ALDS | |
| 2004 | 162 | 92 | 70 | .568 | 1st in American League Central | 1 | 3 | .250 | Lost in ALDS | |
| 2005 | 162 | 83 | 79 | .512 | 3rd in American League Central | - | - | - | - | |
| 2006 | 162 | 96 | 66 | .593 | 1st in American League Central | 0 | 3 | .000 | Lost in ALDS | |
| 2007 | 162 | 79 | 83 | .488 | 3rd in American League Central | - | - | - | - | |
| 2008 | 163 | 88 | 75 | .540 | 2nd in American League Central | - | - | - | - | |
| Total | 1130 | 621 | 509 | .550 | 6 | 15 | .286 | |||