State College Spikes
Thomas signed with the Cardinals and made his professional debut with the State College Spikes of the Class A Short Season New York–Penn League before being promoted to the Peoria Chiefs of the Class A Midwest League in July. Over 43 innings pitched between the two clubs, he went 4-1 with a 3.77 ERA. To begin the 2021 season, he was assigned to the Springfield Cardinals of the Double-A Central. After compiling a 4.87 ERA over innings, he was promoted to the Memphis Redbirds of the Triple-A East.