2008-09: Mike Connolly skated in 43 games for the University of Minnesota-Duluth as a freshman. He was named to the WCHA's All-Rookie Team after scoring 13 goals with 29 assists. He finished +11 with 53 PMs and scored five power play goals for the Bulldogs. UM-D finished seventh in the regular season but won the conference tournament, defeating Denver, 4-0, in the championship game to earn an NCAA bid. In an amazing come-from-behind win against Princeton in the NCAA West Regional, Connolly scored an overtime game-winning goal after assisting on the two last minute goals that the Bulldogs scored with the goalie pulled to tie the game.
2009-10: Connolly was the fourth-leading scorer for Minnesota-Duluth as a sophomore. Playing on the team's top line he scored 14 goals, including five game-winners, and had 26 assists with 24 PMs and an even plus/minus. The Bulldogs tied for fourth in the WCHA but failed to match their playoff run from a year earlier – losing to North Dakota in the WCHA Quarterfinals.
2010-11: Connolly was a finalist for college hockey's Hobey Baker award and was voted team MVP by his teammates as a junior following the Bulldogs' NCAA championship season. Connolly scored 28 goals with 26 assists and was +22 with 59 PMs in 42 games. After finishing fourth in the WCHA during the regular season and losing to Bemidji State in overtime in the WCHA tournament, the Bulldogs shutout Union, 2-0, and then had one-goal wins over Yale, Notre Dame and Michigan, the last in overtime, to capture the NCAA Championship. Connolly signed a two-year, entry-level contract with the Sharks in April 2011, foregoing his senior year of college hockey.
2011-12: Obtained by Colorado in a February 2012 trade with the Sharks, Connolly made his NHL debut with Colorado in March – skating in two games and finishing with no points and 2 penalty minutes. He spent the bulk of the season in the AHL. In 40 games with the Worchester Sharks he scored 10 goals with 20 assists and was +4 with 26 penalty minutes. In 13 games with Colorado AHL affiliate Lake Erie he had 3 goals with 4 assists and was +4 with 4 penalty minutes. The Monsters finished third in the North Division, one point behind Rochester and Houston for the final Western Conference playoff spot.
2012-13: Connolly skated for the AHL's Lake Erie Monsters in his second pro season. He scored 9 goals with 23 assists and was -3 with 21 penalty minutes. Lake Erie finished third in the North Division but missed the AHL playoffs. Connolly was not tendered a contract offer by the Avalanche and in July signed a contract to play with the Augsburger Panther in Germany in 2013-14.
Connolly has signed to play in the DEL for the 2013-14 season.