Fields appeared in small roles in 1930s film comedies and sometimes received screen credits as a writer and assistant director. In 1944, he began working with Abbott and Costello, first in the film In Society (1944) and as a writer/performer on their radio series, where he introduced his Professor Melonhead character. From 1951 he supported Abbott and Costello on NBC-TV's "The Colgate Comedy Hour", and in 1952, he was cast in the team's filmed series, "The Abbott and Costello Show". He also wrote the majority of scripts for the first season.