Nixon died due to complications from Parkinson's disease and a recent stroke, ABC News
"I am devastated to learn that we have lost Agnes," former "All My Children" star Susan Lucci wrote on Instagram. "I adored her and admired her--and I am forever grateful to her!"
Robert A. Iger, chairman and CEO of The Walt Disney Company, called Nixon a "television pioneer."
"Agnes' impact on daytime television and pop culture is undeniable," he said in a statement via ABC. "She was the first to champion socially relevant topics, and the towns and characters Agnes brought to life leave an indelible imprint on television that will be remembered forever."
Nixon got her start in soaps writing for CBS's "Search for Tomorrow" in 1951. Writing stints on "As the World Turns," "The Guiding Light" and "Another World" followed.
In 1968, her show "One Life to Live" debuted and "All My Children," another of her creations, followed two years later.
She debuted "Loving" on ABC in 1983. It ran until 1995 and spawned a spin-off called "The City."
Nixon is credited for bringing important social topics to her daytime shows, with episodes about uterine cancer, abuse and interracial relationships.
Nixon became known as the "queen of Soap Opera writing."
Over the years, she amassed nine Daytime Emmy writing nominations and four wins, as well as a Lifetime Achievement Award.
"All My Children" ended in 2011 and "One Life to Live" concluded the next year. Both shows had a brief return online in 2013, but that effort lasted only one season.