Thomas studied church music under Grabner and Straube in Leipzig and composition under Arnold Mendelssohn in Darmstadt. In 1921, he became an instructor of theory at the Leipzig Conservatory and in 1928 the choir master at the Institute of Church Music. He went on to a distinguished career in choir training and conducting and teaching, holding posts in Berlin, Frankfurt, Detmold, and most notably as director of the Thomaskantorei and the Thomasschule in Leipzig from 1955-61. In 1961, he left East Germany for Cologne to direct the Cologne Bach Society concerts and eventually to return to his old post in Frankfurt. His textbook Lehrbuch der Chorleitung (Textbook for Choral Conducting) is still considered a classic work on the subject.