Gantner grew up in Eden, Wisconsin,^[1] and attended Campbellsport High School in nearby Campbellsport.^[1] He played his college baseball at the University of Wisconsin–Oshkosh, where he was enshrined into the Titans' Hall of Fame in 1984.

Gantner was a 12th-round draft pick in the 1974 amateur draft. He spent two years in the minor leagues before being called up to the majors. Ganter was best known for his consistent play, which culminated in a respectable .274 career batting average after 17 seasons. He comprised a stellar infield throughout much of the 1980s beside Hall of Famers Robin Yount at shortstop, Paul Molitor at third base, and Cecil Cooper at first base. Gantner, or "Gumby" as he was affectionately known because of the way he turned double plays, was the Brewers’ second baseman when they won the 1982 American League pennant. Gantner scored the go-ahead and ultimate winning run in the bottom of the seventh inning of the fifth and decisive game of the ALCS, scoring behind Charlie Moore on Cooper's RBI single. Unfortunately for Jim and the rest of the team, the Brewers fell in seven games to the St. Louis Cardinals in the World Series, the franchise's lone World Series appearance to date.

Gantner rarely hit home runs. On September 3, 1991, he hit his first home run since 1987, ending a streak of 1,762 at-bats without one. Gantner's last career home run came on August 14, 1992, in the 13th inning, against Boston Red Sox reliever Jeff Reardon. Gantner hit the first pitch into the right field bleachers in Milwaukee County Stadium, giving the Brewers an 8-7 victory. Brewers announcer Bob Uecker had the call with, "Here's the pitch to Gantner. He hits one to right and deep. Get up. Get up. Get outta here - gone! A dinger for Klinger! And this game is over. Woah, Jimmy Gantner!"

Gantner pitched an inning of relief against the Kansas City Royals on August 29, 1979, allowing two hits. Despite the game being a blowout, he was almost ejected for arguing balls and strikes with the umpire.

In his rookie season, Gantner pinch-ran for Hank Aaron in Aaron's final Major League game on October 3, 1976.^[2]

Gantner was elected to the Wisconsin Athletic Hall of Fame in 2005.

Gantner coached several years after he retired as a player. He was a silent partner of Hale Park Automotive Services in Hales Corners, Wisconsin. He also is employed by the Brewers' organization. Jim also is partial owner of a bar in Eden, Wisconsin, called "Scuds Buds."

Gantner entered his first season as field manager of the Wisconsin Woodchucks in the Northwoods League in 2007.^[3]

Hitting

He had a career .985 fielding percentage at second base and a .956 fielding percentage at third base, his two primary positions.

• List of Major League Baseball players who spent their entire career with one franchise

• Career statistics and player information from MLB, or ESPN, or Baseball Reference, or Fangraphs, or Baseball Reference (Minors)