In his freshman season with the Michigan State Spartans, he played in 36 games and finished second amongst the teams rookies in points.

[6] On March 30, 2016, he chose to forego his senior season at Michigan State and sign a two-year entry-level contract with the St. Louis Blues.

[5] MacEachern began his professional career during the 2016–17 season with the Blues' American Hockey League (AHL) affiliate, the Chicago Wolves.

[18] As a free agent from the Blues, MacEachern was signed to a one-year, two-way contract with the Carolina Hurricanes on July 15, 2022.

[19] On July 1, 2023, MacEachern signed as a free agent to a two-year, one-way $1.55 million contract to return to the Blues.