She died peacefully with her family by her side at her home in Plains, Georgia, according to the Carter Center, a not-for-profit organization founded by her husband and former president Jimmy Carter, 99.
They were married for 77 years.
Mrs Carter had been suffering from dementia.
“Rosalynn was my equal partner in everything I ever accomplished,” Mr Carter said.
“She gave me wise guidance and encouragement when I needed it. As long as Rosalynn was in the world, I always knew somebody loved and supported me.”
Unlike many previous first ladies, Rosalynn Carter sat in on cabinet meetings and represented her husband on foreign trips.
In 1977, only months into his presidency, Mr Carter sent her to Latin America to tell dictators he was serious about denying military aid and other support to people who violated human rights.