Read Rosalynn Carter’s full obituary.

Rosalynn Carter, a true life partner to Jimmy Carter who helped propel him from rural Georgia to the White House in a single decade and became the most politically active first lady since Eleanor Roosevelt, died on Nov. 19 in Plains, Ga. She was 96.

The Carter Center in Atlanta announced her death. It had disclosed on May 30 that Mrs. Carter had dementia. “She continues to live happily at home with her husband, enjoying spring in Plains and visits with loved ones,” a statement by the center said at the time. On Friday, the center said she had entered hospice care at home.

Mrs. Carter was the second longest-lived first lady; Bess Truman, the widow of President Harry S. Truman, was 97 when she died in 1982.

Over their nearly eight decades together, Mr. and Mrs. Carter forged the closest of bonds, developing a personal and professional symbiosis remarkable for its sheer longevity.

Their extraordinary union began formally with their marriage in 1946, but, in a manner of speaking, it began long before that, with a touch of kismet, just after Rosalynn (pronounced ROSE-a-lynn) was born in Plains in 1927.

She had been delivered by Mr. Carter’s mother, a nurse. And a few days later, in a scene that might have been concocted by Hollywood, his mother took little Jimmy to Rosalynn’s house, where he “peeked into the cradle to see the newest baby on the street,” as he recalled in his 2015 memoir, “A Full Life, Reflections at Ninety.”

He was not quite 3. Eighteen years would pass before the two would truly connect. But once they did, they became life and work partners, melding so completely that as president Mr. Carter would call her “an almost equal extension of myself.”