She died peacefully with her family by her side, the Carter Center said in a statement.
In May 2023, the Carter family had said she had dementia but was continuing to live happily at the couple's home in Plains, Georgia.
On Friday, it was reported that she had entered a hospice care home in Georgia, and was spending time with her 99-year-old husband, who has been in hospice care since February.
The veteran women's rights campaigner was married to President Carter for 77 years, making them the longest-married first couple.
“Rosalynn was my equal partner in everything I ever accomplished," Mr Carter said in a statement.
“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."
Mrs Carter was known as a campaigning first lady, sitting in on Cabinet meetings, speaking out on controversial issues and representing her husband on foreign trips.
When her role in a highly publicised Cabinet shake-up became known, she was forced to declare publicly: “I am not running the government."
Both Carters said in their later years that Rosalynn had always been the more political of the two.
She championed mental health and problems of the elderly as her signature policy emphasis while her husband was in the White House, and criticised reporters who did not cover those issues as much as she believed was warranted.
During the Iranian hostage crisis - in which American diplomats and others were held captive in Tehran after the Islamic revolution - when Carter was seeking re-election, Rosalynn sought to support her husband by speaking in 112 cities in 34 states during a 44-day tour.
Her speeches and forays into crowds were credited with helping Carter defeat Democratic challenger Ted Kennedy in the 1980 primaries, although he went on to lose overwhelmingly to Ronald Reagan in the general election.