Mrs Bush was the wife of the 41st president, George H W Bush, and mother of the 43rd, George W Bush.
The Bush family had said in a statement on Sunday that she was in failing health, had decided not to seek further medical treatment and instead would focus on “comfort care.”
According to some media reports, Bush had been battling chronic obstructive pulmonary disease and congestive heart problems in recent years.
“Barbara Bush was a fabulous First Lady and a woman unlike any other who brought levity, love and literacy to millions,” George W Bush said in a statement.
“To us, she was so much more. Mom kept us on our toes and kept us laughing until the end.”
President Donald Trump and former Democratic Presidents Barack Obama and Bill Clinton were among those praising the late First Lady.
“She will be long remembered for her strong devotion to country and family, both of which she served unfailingly well,” Trump and his wife, Melania, said in a statement that noted Bush’s championing of literacy “as a fundamental family value.”
Clinton, who defeated her husband in the 1992 presidential election, called Mrs Bush “fierce and feisty in support of her family and friends, her country and her causes. She showed us what an honest, vibrant, full life looks like.”
Obama and his wife, Michelle, said in a statement that Barbara Bush was “an example of the humility and decency that reflects the very best of the American spirit.”
Barbara Bush was First Lady when her husband was in the White House from 1989 to 1993. Her son, Republican George Walker Bush, triumphed in the disputed 2000 US election and was president from 2001 to 2009.
The only other woman to be both wife and mother of US presidents was Abigail Adams, the first lady from 1797 to 1801. She died before son John Quincy Adams was elected president in 1824.
Dubbed “The Silver Fox” by her husband and children, Barbara Bush was known for her snow-white hair and for being fiercely protective of her family.
She had an independent streak and could be sharp-tongued. As First Lady, she promoted literacy and reading.
But she discouraged speculation that she wielded political influence with the president like her predecessors – Ronald Reagan’s wife, Nancy Reagan, and Jimmy Carter’s wife, Rosalynn Carter.
“I don’t fool around with his office and he doesn’t fool around with my household,” she once said.
Barbara Bush sometimes made biting remarks, particularly when she felt the need to defend her husband. One notable example came in 1984 when George H W Bush was seeking re-election as vice president under Reagan.
She told reporters that Geraldine Ferraro, her husband’s Democratic rival for the vice presidency, was a “$4 million … I can’t say it but it rhymes with ‘rich.’”
She apologised to Ferraro, the first woman running for US vice president on a major-party ticket.
Bush generally refused to discuss publicly her personal views on controversial topics such as abortion, an issue on which she was believed to differ from her husband’s more conservative stance.
Opinion polls often showed her popularity as first lady exceeding her husband’s as president. “I don’t threaten anyone,” she said. “That’s because I’m everyone’s grandma.”
She was born Barbara Pierce on June 8, 1925, and grew up in Rye, New York. Her father was Marvin Pierce, publisher of McCall’s magazine.
She was home from boarding school in 1941 when she met her future husband at a Christmas party in Connecticut. She dropped out of prestigious Smith College to marry Bush, then a young naval aviator home on leave from World War Two.
The Bushes had six children – George W, Jeb, Neil and Marvin and daughter Dorothy. A daughter, Robin, died of leukemia in 1953 at age three. Barbara Bush’s hair began to turn prematurely white after the shock of the girl’s death.
Jeb, Bush served as governor of Florida from 1999 to 2007, and sought the 2016 Republican presidential nomination and she campaigned for him before he dropped out of the race.
The Bushes married on January 6, 1945, and Barbara set up households in numerous cities as her husband moved from being a Texas oilman to being a member of Congress, Republican Party leader, US envoy to China and the United Nations and head of the Central Intelligence Agency.
The Bushes celebrated their 73rd wedding anniversary in January.
George HW Bush said marrying Barbara, whom he called “Bar,” was “the thing I did right.”
– Reuters
