Thomas spent his first professional season with the Arizona League Diamondbacks and Missoula Osprey,[5] batting .333 with two home runs, 27 RBIs, and 12 stolen bases in 56 games between the two teams.[5] He started 2019 with the Kane County Cougars.[6][7][8] In July, he was selected to play in the All-Star Futures Game.[9] In August, he was promoted to the Visalia Rawhide, with whom he finished the year.[10] Over 114 games between the two teams, Thomas slashed .300/.379/.450 with ten home runs, 55 RBIs, and 15 stolen bases.
Thomas did not play a minor league game in 2020 due to the cancellation of the minor league season caused by the COVID-19 pandemic.[11] He began the 2021 season with the Amarillo Sod Poodles.[12] In June, Thomas was selected to play in the All-Star Futures Game.[13] He was promoted to the Reno Aces in August.[14] Over 106 games between the two teams, he slashed .313/.394/.559 with 18 home runs, 59 RBIs, and 29 doubles.[15][16][17] He opened the 2022 season back with Reno, and hitting .277/.362/.495/.857 with 4 home runs and 14 RBI over 24 games.[18]
On May 8, 2022, Thomas was promoted to the major leagues for the first time.[19] On May 11, he hit his first career home run off Sandy Alcántara of the Miami Marlins.[20]
In Game 4 of the 2023 National League Championship Series, Thomas hit a pinch-hit, game-tying two-run home run in the eighth inning to help propel the Diamondbacks to a 6–5 victory.[21]
Thomas' father Allen was the longtime strength and conditioning coach of the Chicago White Sox. His mother Marcella "has roots" in Sonora and Thomas has family in Agua Prieta.[22]