She began her career in the early 1970s in an episode of The Streets of San Francisco. Throughout the 1970s and 1980s she starred in numerous television shows and commercials, the horror film Nightmare in Blood (1978), and popular made-for-TV movies such as Vampire (1979), Moviola: The Scarlett O'Hara War (1980) in which she portrayed Joan Crawford, and It Came Upon the Midnight Clear (1984).
As of 2011, she is President of the California corporation To Be Announced, Inc., founded November 20, 1978.
Youngfellow is perhaps best known for her role as sharp-tonged and sarcastic waitress Jan Hoffmeyer Gray on the sitcom It's a Living, which ran from 1980 until 1982 on ABC, and from 1985 to 1989 in first-run syndication (she, along with Gail Edwards, Paul Kreppel and Marian Mercer, were the only members of the It's a Living cast to last all the way through the show's network and syndication runs).
She is the wife of stage and screen actor Sam Freed, whom she married in 1983.
In 1990, It's a Living producers Paul Junger Witt and Tony Thomas cast Youngfellow in the pilot episode of Blossom, in which she played the mother of Mayim Bialik's title character; she did not continue with the project when NBC picked it up as a regular series. In 1998, Youngfellow made her last TV appearance, in an episode of Law & Order.
The two narrated the 2001 audiobook of The Children's Book of Faith by william J. Bennett. Youngfellow was formerly married to Michael Mund Youngfellow from 1968 to 1975.
