Wagner died Saturday at her home in New York's Hudson Valley, the network announced. The cause was not given.
Wagner opened "As the World Turns" when it premiered on April 2, 1956, with the words: "Good morning, Dear." The show's production company, TeleNext Media Inc., said she held the Guinness World Record for playing the same role on television for the longest amount of time, 54 years.
Wagner was seen less often in later decades, but no other network TV performer came close to her run playing a single character.
She was still part of the cast, though with a small presence, in December 2009 when CBS announced that "As the World Turns" was being canceled. Its last episode will air in September.
Her final appearance aired April 5, in an episode in which Julianne Moore, a series regular in the 1980s whose two half-sister characters were Wagner's granddaughters, returned for a guest walk-on. The episode was taped in March.
In interviews, Wagner often called Nancy "a tent-pole character."
"Nothing ever happens to Nancy," Wagner said. "She's the one the others come and talk to."
Born in 1918 in Lubbock, Texas, Wagner studied drama and music at Monmouth College in Illinois, graduating in 1938. She appeared on Broadway in the 1940s, including a small role in the musical "Oklahoma!" and in off-Broadway and summer stock productions.
Before being cast on "As the World Turns," she appeared on early TV shows such as "The Philco Television Playhouse" and "The World of Mr. Sweeney."
She married producer Robert Willey in 1954, and over the years he served as her manager and agent as well as producing some of her stage appearances. He died in 2009.