The network said the veteran daytime drama star died Thursday at her home in Virginia.
Fickett had been an original cast member of "All My Children." It premiered in 1970. In 1973, she became the first performer to receive an Emmy Award for work on a daytime soap opera.
The Bronxville, N.Y. native had been a seasoned stage, film and TV actress before she joined the soap opera. In 1958, she was nominated for a Tony Award for her Broadway role as Eleanor Roosevelt in "Sunrise at Campobello."
ABC plans to dedicate the Sept. 21 episode of "All My Children" to Fickett. Two days later, the series will end its network run.
In a statement released Monday, ABC said "we cannot help but recognize and remember Mary's wonderful depiction of Pine Valley's revered Ruth." The network added that Fickett's character's marriage to Dr. Joe Martin was "always a stabilizing force that represented 'home' for many."
Cast member Michael E. Knight, who played Fickett's son Tad on the show, said he was grateful for having worked with Fickett, calling her a "dear friend" and "incredible actress."
"My thoughts and prayers go out to her family and friends at such a difficult time. She was dearly loved by so many many people," Knight said in a statement.
Fickett is survived by a daughter and a son and several grandchildren and great-grandchildren.
The Associated Press contributed to this report.