Born Patricia Davidson in Jacksonville, Florida, Darbo grew up in Atlanta, Georgia. She studied theater at Georgia Southern University in Statesboro, Georgia, graduating in 1970, and undertook further study at the Atlanta School of Drama. Darbo worked as a credit manager until 1984, when she began a professional acting career.
By 1991, Darbo had featured in numerous stage, film and television credits and was contracted to the ABC network. In 1991, the Los Angeles Times reported that Darbo was undertaking a personal campaign to seek nomination for an Academy Award for Best Supporting Actress for her role in Daddy's Dyin': Who's Got the Will?.
Darbo appeared as Penny Baker on Step by Step (1991–1992). In 1994, she starred as Roseanne Barr in an NBC television movie, Roseanne and Tom: Behind the Scenes. She also starred as Miss Spencer in the 1998 made-for-TV-film Ruby Bridges. From 1998 to 2005, Darbo played Nancy Wesley on the NBC soap opera Days of our Lives.
Darbo was a guest star in two Seinfeld episodes; The Revenge in 1991 and The Sniffing Accountant in 1993. Later, in 2010, she also guest starred in Showtime's Dexter as a landlady.
Darbo has been married to director Rolf Peter Darbo since 1973.