The court announced her death in a statement Friday morning, citing "complications related to advanced dementia, probably Alzheimer's, and a respiratory illness." She was 93.
[Ads /]
O'Connor was the first woman to serve on the nation's highest court, shattering two centuries of male-dominated jurisprudence with widely celebrated poise, humanity and independence.
SEE ALSO: Retired Justice Sandra Day O'Connor, the first woman on the Supreme Court, has died at age 93
Retired Justice Sandra Day O'Connor, the first woman on the Supreme Court, has died at age 93
Historians consider her one of the most consequential women in American history.
"The law was a male thing. The Supreme Court was a male place. Merely her presence there as a woman changed everything," said Evan Thomas, O'Connor's official biographer.
[Ads /]
Republican President Ronald Reagan appointed O'Connor in 1981 as, "truly a person for all seasons," a constitutional conservative who he believed would both solidify the court's right-leaning majority and fulfill a campaign promise to put a qualified woman on the bench.
"The proper role of the judiciary is one of interpreting and applying the law -- not making it," O'Connor, then 51, said during her confirmation hearing. She was confirmed by the Senate 99-0.
For more than two decades, O'Connor was often the decisive vote on a narrowly divided court. She wrote landmark opinions on abortion and affirmative action, and is credited by some -- bitterly blamed by others -- for helping Republican George W. Bush secure the presidency in the contested 2000 election.
For so many women in the legal field, including Drexel University professor Lisa Tucker, this loss is personal.
"Justice O'Connor thought this idea that she was a swing vote made it sound like she could be persuaded with legal arguments that she did not agree with. She thought real integrity of decision-making was looking at the facts in every case," said Tucker.
[Ads /]
While a law student, Tucker coauthored a book with O'Connor and her then 9-year-old granddaughter, titled "Meet My Grandmother: She's a Supreme Court Justice."
The children's book had pictures of O'Connor at work and doing everyday things around Washington D.C.
"She later said it was one of her favorite books that anyone ever wrote about her because it really touched the personal side of her. It was really one of the pinnacles of my life," said Tucker. "When my first daughter was born, she wrote me a letter and said this will change your life in marvelous unexpected ways."
The former justice is survived by her three sons.
Funeral plans have not yet been announced.
ABC News contributed to this report.