[4] After signing, Chalmers made his professional debut for the Arizona League Athletics where he posted a 0–1 record with a 2.66 ERA in 11 starts.
In 2019, he began the year rehabbing before being assigned to the Fort Myers Miracle, with whom he started five games, pitching to a 1–1 record with a 3.38 ERA.
[9] Chalmers was assigned to the Double-A Wichita Wind Surge, but struggled to a 9.49 ERA in 12.1 innings of work.
[11] On June 11, Chalmers was designated for assignment by the Cubs without appearing in a major or minor league game for the organization.
[17] On August 19, 2022, Chalmers signed with the Gastonia Honey Hunters of the Atlantic League of Professional Baseball.
[19] On July 2, 2024, Chalmers signed with the High Point Rockers of the Atlantic League of Professional Baseball.