Born in Akron, Ohio, she graduated from the University of Michigan, then spent several seasons working in summer stock. She made her Broadway debut in the chorus of the short-lived musical, Greenwillow in 1960.
She drew critical notice for her performance in New Faces of 1962, and won the Tony Award for Best Featured Actress in a Musical, the Drama Desk Award for Outstanding Performance, and the Theatre World Award for her performance as Marge MacDougall in Promises, Promises (1968). Additional theatre credits include Hay Fever and the short-lived 1978 revival of Stop the World – I Want to Get Off with Sammy Davis, Jr. In 1979, she starred as Deirdre in Bosoms and Neglect.
She made guest appearances on such shows as Love, American Style; Archie Bunker's Place; Mama's Family; Benson; The Golden Girls; Murder, She Wrote; Touched by an Angel; and Suddenly Susan, among many others. She had featured roles in the television movies The Cracker Factory (1979), which starred Natalie Wood, and Murder in Three Acts (1986), starring Peter Ustinov and Tony Curtis. Her big screen credits include John and Mary (1969); Oh, God! Book II (1980); and 9 to 5 (1980), where she played Missy Hart, the sweet-natured wife of misanthropic corporate executive Franklin Hart (Dabney Coleman).
Mercer was a resident of the Motion Picture & Television Country House and Hospital in Woodland Hills, California until shortly before her death, on April 27, 2011, from Alzheimer's disease, in Newbury Park, California, at the age of 75. She was survived by her second husband; her daughter, Deidre Whitaker; and a sister.
