Kelly was born in Graceville, Minnesota, and grew up in Sayreville, New Jersey, attending St. Mary's High School in nearby South Amboy.

Prior to the start of the 1976 season, Kelly was purchased by the Baltimore Orioles and assigned to the Triple-A Rochester Red Wings; he would not return to the major leagues as an active player.

Kelly was the 11th pilot of the Twins since they moved to Minneapolis–Saint Paul from Washington in 1961, and his 15-plus-year-stint as manager is the longest consecutive-season managerial term in the team's history, which began with the founding of the American League in 1901.

Though the '87 Twins were criticized for being the top team in a weak division (amassing only a .525 record in regular season play, which was the worst winning percentage for an eventual World Champion until surpassed by the St. Louis Cardinals in 2006), they easily handled the Detroit Tigers in five games, losing only Game 3 of the American League Championship Series to a heartbreaking 8th-inning two-run home run.

The World Series was a well-fought contest between the Twins and the National League champion St. Louis Cardinals, each team winning all of its home games.

In the AL Championship, the Twins easily beat the Toronto Blue Jays in 5 games, winning the right to face the Atlanta Braves in the World Series.

[6] Although he was being facetious, the grueling Game 3 proved Kelly prescient as a series of double switches and substitutions emptied the Twins' bench and both teams' bullpens.

Kelly was forced to pinch hit Rick Aguilera in the top of the 12th and was prepared to send outfielder Dan Gladden to the mound if necessary; however, the Braves won in the bottom of the 12th when David Justice narrowly beat a throw to the plate.

Game 6 featured two climactic plays by Kirby Puckett who, in the top of the 3rd, made a sensational leaping catch against the center field acrylic glass to prevent a Braves' run.

"[7] Morris ended up pitching 10 scoreless innings as the Twins won 1–0 in the bottom of the 10th, giving Minnesota its second World Series victory in five years.