The former justice served from 1981 until 2006, during a time of transition for the nation’s highest court.

In a statement on Friday, the court said that O’Connor died in Phoenix, Arizona, from complications related to dementia and respiratory illness. She served on the Court from 1981 until 2006.

“A daughter of the American Southwest, Sandra Day O’Connor blazed a historic trail as our Nation’s first female Justice,” Chief Justice John Roberts said in the statement.

O’Connor was appointed by Republican former President Ronald Reagan in the early 1980s, as the United States began a shift to the right and conservative groups fought to transform the country’s judicial landscape in their favour.

The former justice was known as a relatively moderate figure, focused on reaching consensus and frustrating critics from both left and right. Her middle-of-the-road approach often made her a key vote in close decisions.

Despite her personal conservatism, O’Connor helped reaffirm the 1973 decision Roe v Wade, which made abortion a constitutional right in the United States.

“Some of us as individuals find abortion offensive to our most basic principles of morality, but that can’t control our decision,” O’Connor said in court, reading a summary of the decision in Planned Parenthood v Casey. “Our obligation is to define the liberty of all, not to mandate our own moral code.”

She was also part of a majority that handed the contested 2000 election to former President George W Bush, in a controversial decision that halted a recount effort that could have reversed Bush’s victory in the key state of Florida.

O’Connor retired in 2006 during Bush’s second term and was replaced with the more rigidly conservative Samuel Alito as the already conservative court continued a shift to the right.

When the Supreme Court, with a 6-3 conservative majority forged after decades of organising by the conservative judicial movement, overturned Roe v Wade in June 2022, Alito authored the majority opinion.