Opting to pursue a collegiate career, O'Connor was selected with the 194th overall pick by the Sioux Falls Stampede in the 2013 United States Hockey League (USHL) Entry Draft.

[5] Embarking on his collegiate career with the Denver Pioneers in the 2015–16 season, O'Connor appeared in 23 games for two goals and two assists as a freshman.

In the following 2016–17 season, he became a fixture among the Pioneers checking line, registering 7 goals and 18 points while appearing in all 44 games to help Denver claim the 2017 national championship.

[7] At the conclusion of his junior season and following the 2018 NHL entry draft, O'Connor was invited to attend the Colorado Avalanche development camp.

[8] On July 24, 2018, O'Connor forwent his senior season as captain with the Pioneers in agreeing to a two-year, entry-level contract as an undrafted free agent with the Avalanche.

[9] O'Connor began the 2018–19 season with the Avalanche's American Hockey League (AHL) affiliate, the Colorado Eagles.