In the late 1920s, Lewis worked as a circus performer, but ultimately decided on college, earning a Ph.D. in child psychology from Columbia University. He taught school and wrote two children's books. In 1949, at the suggestion of a friend, Lewis turned to acting and joined the Paul Mann Actor's Workshop in New York. Lewis worked in burlesque and vaudeville theaters across the country, which eventually led to Broadway. By the 1950s, television was booming, and Lewis took advantage of the work appearing on almost every live show out of his home base of New York City. His most famous regular TV roles were Officer Leo Schnauser on Car 54, Where Are You? (1961) and Grandpa on The Munsters (1964). When these shows ended, he opened a restaurant in New York called "Grampa's" in Greenwich Village. He has since produced a home video for children and appeared on WTBS in a series of Saturday morning programs for children.