A mild-mannered jurist who thinks carefully before she speaks or makes decisions, Sandra Day O'Connor does not project the figure of a trailblazer. But she became exactly that. She was the daughter of cattle ranchers Henry Day and Ada Wilkey. She was a true child of the frontier, learning how to brand cattle and run a household on her parents' 155,000 acre ranch. She later wrote about her childhood in the autobiography "Lazy B: Growing up on a Cattle Ranch in the American Southwest." But when she became of school age, her parents sent her to El Paso to live with her maternal grandmother, Mamie Scott Wilkey, who she said had the greatest influence on her life. In school, she was a high achiever and graduated from high school at the age of 16, then she graduated from Stanford Law School third in a class of 102. Ironically, the valedictorian was future fellow Supreme Court Justice William Rehnquist, whom she briefly dated. She married in 1952 and sought work in major law firms. But women lawyers were a rarity in those days and she worked as a prosecutor in some county offices. She then established her own private practice in Phoenix in 1960, and became involved in Republican politics. In 1965, she was appointed Assistant Attorney General for the state of Arizona. Her life changed in 1969, when she was appointed to the Arizona state Senate to fill a vacant seat, and she was reelected. She was well-regarded by her colleagues and 1973, she became the first woman in the nation to become Majority Leader in an American state Senate. However, her passion was for law rather than politics and in 1975, she was elected Maricopa County Superior Court Judge. She served with distinction and in 1979, Democratic Governor Bruce Babbitt appointed her to the state Court of Appeals, in spite of her being a Republican. She served with distinction again and came to the attention of U.S. Senator Barry Goldwater, who regarded her very highly.

She became a national figure in 1981. The year before, Ronald Reagan had been elected President and had promised to appoint a woman to the U.S. Supreme Court. A member of the high court, Associate Justice Potter Stewart, announced his retirement, and the Reagan Administration considered several female Federal judges among who to choose. However, Goldwater brought O'Connor to Reagan's attention, and she visited him at the White House. Reagan himself owned a ranch and had a real affiliation for the frontier, and O'Connor's background and passion for the American southwest made a positive impression on him. Still, as a little-known state judge who was considered legalistic and aloof on the bench, she was not thought to be a likely choice, and she was as surprised as anyone when Reagan nominated her. Her nomination drew bipartisan praise and she was confirmed unanimously.

In her first years on the U.S. Suprene Court, she was surprised by the amount of scrutiny she received. However, she enjoyed serving with her longtime friend William Rehnquist, who became Chief Justice in 1985. She compiled a moderate to conservative record on the court while ruling each case as narrowly as possible, avoiding setting precedent. She also sought to avoid the limelight. However, in 1989, the court became the center of national attention and O'Connor the center of that attention. The case was Webster vs. Reproductive Health Services, in which the state of Missouri enacted several restrictions on the practice of abortion, which had become legalized by the court in 1973. Previous rulings had claimed that any limits on abortions were unconstitutional. Supporters of abortion wanted a similar ruling, while conservatives hoped that Roe vs. Wade, which had legalized abortion, would be overturned. Instead, the court refused to overturn Roe vs. Wade, but also ruled that the contested restrictions on abortion were allowed by that same ruling. The 9 member court voted 5 to 4 on that, and O'Connor was the deciding vote and the author of the final ruling. No one concerned about the issue was satisfied by the ruling. In subsequent years, the makeup of the Supreme Court changed significantly and she became its second most senior member. In 1993, she was pleased when another woman was appointed to the court, even though that woman, Ruth Bader Ginsburg, was considerably more liberal than she. During many of her later years on the court, she was the deciding vote of many 5 to 4 decisions and was regarded as the swing vote on rulings that conservatives and liberals disagreed on. However, she continued to to avoid the limelight, and would often become upset when the court became the center of criticism and controversy.

In 2005, her husband was seriously ill. Her longtime friend Rehnquest was also ill and planning to retire. But out of deference to O'Connor, he delayed his retirement announcement so that she could retire first. She announced that she would step down from the court as soon as her successor was sworn in. She had mixed feelings when President George W. Bush announced that he would appoint Federal Appeals Judge John Roberts. O'Connor regarded Roberts highly and had great respect for his abilities, but having faced gender discrimination for so much of her career had hoped that another woman would be appointed to replace her. A short time later, she was saddened by the death of Rehnquest. Bush decided to appoint Roberts as Chief Justice and nominated White House Counsel Harriet Miers to succeed O'Connor, but Miers withdrew after her nomination drew charges of crony-ism and attacks on her qualifications. Bush then nominated longtime Federal Appeals Court Samuel Alito, a conservative former U.S Attorney of New Jersey. Alito was confirmed by the Senate after a contentious debate. O'Connor's retirement was interrupted when she was appointed by Bush to the Iraq Study Group, which made recommendations on how to end the Iraq War.

Many who covered her career noted that in her early years on the court, she usually supported the conservative faction, but became the swing vote later on, and they claimed that she changed and became more liberal. In fact, it was the court itself that changed more than she did. When she was appointed, the court included strong liberals William Brennen, Thurgood Marshall, and Harry Blackman, all of whom left in the early 1990s. During her later years on the court, she served with Antonin Scalia and Clarence Thomas, strong conservatives, and the different composition of the court altered both the tone and substance of its rulings, and made liberal groups less inclined to seek redress from it.