Thomas was the down judge in Sunday's divisional round game between New England and the Los Angeles Chargers. That's a first, according to the league's Twitter account.
Thomas was hired in 2015 and was already the league's first female full-time official. Before that, she was the first woman to officiate a college football bowl game.
Terri Valenti was the replay official in Saturday's playoff game between the Chiefs and Colts, also a first.
KTRK contributed to this report.