Former US first lady Rosalynn Carter, longtime wife of Jimmy Carter ...

Former US first lady Rosalynn Carter, who was married to president Jimmy Carter for 77 years, has died.

Key points:Rosalynn Carter "died peacefully with her family by her side", according to a statementThe former first lady married Jimmy Carter in 1946, when she was 18Mr Carter says she was "my equal partner in everything I ever accomplished"

She died peacefully with her family by her side, a statement from the Carter Center said.

"Rosalynn was my equal partner in everything I ever accomplished," Mr Carter said in the 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."

In May 2023, the Carter family said Ms Carter had dementia but was continuing to live happily at the couple's home in Plains, Georgia.

Jimmy and Rosalynn Carter were the longest-married presidential couple, having wed in 1946 when he was 21 and she was 18.

Ms Carter had four children with Mr Carter. Earlier this year, 99-year-old Mr Carter entered hospice care.

Jimmy Carter and Rosalynn Carter celebrated their 75th wedding anniversary in Plains, Georgia in July, 2021.(Reuters: John Bazemore)

'My closest adviser'

In Washington, the Carters were a team, with the president calling Ms Carter "an extension of myself" and "my closest adviser". She was often invited to sit in as an observer at cabinet meetings and political strategy discussions.

In a 1978 interview with magazine editors, Mr Carter said he shared almost everything with his wife except top-secret material.

"I think she understands the consciousness of the American people and their attitudes perhaps better than do I," he said.

The first lady also was sent on important official missions to Latin America and was part of the unsuccessful campaign for ratification of the Equal Rights Amendment to the US Constitution to ensure equal treatment of women under the law.

The Iranian hostage crisis — in which American diplomats and others were held captive in Tehran after the Islamic revolution — occurred when Mr Carter was seeking re-election. The crisis contributed to the downfall of his presidency as he refrained from campaigning while trying to resolve the stand-off.

The Carters were widely recognised for their humanitarian work in the decades after they occupied the White House.(AP: Mark Humphrey)

During that time, Ms Carter 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 Mr Carter defeat Democratic challenger Ted Kennedy in the 1980 primaries, although he went on to lose overwhelmingly to Ronald Reagan in the general election.

After his single term in office ended in 1981, Mr Carter also enjoyed more post-White House years than any president before him, and Ms Carter played an instrumental role during those years, including as part of the nonprofit Carter Center and the Habitat for Humanity charity.

"The best thing I ever did was marry Rosalynn," the former president said in 2015.

"That's the pinnacle of my life."

An advocate for human rights, childhood immunisation and mental health

Ms Carter's interest in mental health issues stemmed from the early 1970s when she began to realise, while helping her husband campaign for governor, the depth of the problem in her home state of Georgia and the reluctance of people to talk about it.

As first lady of Georgia, she was a member of a governor's commission to improve services for the mentally ill.

In the White House, she became honorary chair of the President's Commission on Mental Health, key to passage of a 1980 act that helped fund local mental health centres.

Rosalynn Carter poses for a half-length portrait in the White House on February 18, 1977.(US Library of Congress via Reuters)

After leaving Washington, she pursued her work through the Carter Center, a private, nonprofit institution the Carters founded in Atlanta in 1982. She continued to advocate for mental health, early childhood immunisation, human rights, conflict resolution and the empowerment of urban communities.

"I hope our legacy continues, more than just as first lady, because the Carter Center has been an integral part of our lives. And our motto is waging peace, fighting disease and building hope," she told C-SPAN in a 2013 interview.

"And I hope that I have contributed something to mental health issues and help improve a little bit the lives of people living with mental illnesses."

Speaking about her 1998 book Helping Someone With Mental Illness, Ms Carter said she longed for the day when the mentally ill would be free from discrimination.

In their post-Washington years, the Carters were also key figures in the Habitat For Humanity charity, helping build homes for needy families. Their humanitarian efforts were crowned in 2002 when Mr Carter was awarded the Nobel Peace Prize.

"I am especially grateful to Rosalynn, who has been a part of everything I've done," Mr Carter said in a speech on the day he learned that he had won the award.

Both Carters were active members of the community in Plains, Georgia, including at the Maranatha Baptist Church where Ms Carer served as a deacon and the former president as a deacon and long-time Sunday school teacher.

Ms Carter was elected to the Gannett Co board of directors in 1983. She published her autobiography, First Lady From Plains, in 1984 and wrote three other books. In 2001, she was inducted into America's National Women's Hall of Fame.

ABC/Reuters