Born Dorothy McNulty, the name under which she was billed until 1938, her first professional performance was as a singer-acrobat in the Broadway musical Good News (1927); the subsequent film version (1930) was her screen debut. However, her film career didn't begin in earnest until 1936, when she began playing comedic supporting roles in numerous films. She became very popular in the title role of the Blondie comedy series (1938-50), based on the comic strip; she also played Blondie on radio for many years. She did little film work after the end of the series, instead devoting herself to union affairs; eventually, she was vice president and executive secretary of AGVA. In the '60s she provided voice-overs for the TV cartoon series The Jetsons. In 1971 she appeared in the Broadway musical No No Nanette. She married producer Robert Sparks.