William O. Douglas is the longest-serving justice in Supreme Court history, with 13,358 days on the bench between 1939 and 1975. Clarence Thomas now sits second on the all-time list of longest serving Supreme Court justices, having passed Stephen Johnson Field’s mark in 2026 after more than 34 years of service. The rest of the top ranks are filled by names that shaped entire eras of American law: John Marshall, John Paul Stevens, Hugo Black, and the first John Marshall Harlan.
The All-Time Rankings
Service is measured from the day a justice took the oath of office to the day they retired, resigned, or died. Only active service on the Supreme Court counts.
- William O. Douglas (1939–1975). 13,358 days, or about 36 years and 209 days. Franklin Roosevelt appointed him at age 40, and he remains the only justice ever to serve more than 36 years. His tenure ran from the New Deal through the Vietnam War period.1Supreme Court Historical Society. Clarence Thomas Poised to Become the Second-Longest Serving Justice
- Clarence Thomas (1991–present). Over 12,615 days and counting. Thomas passed Field’s total in 2026. If he stays on the bench, he would surpass Douglas’s record in May 2028.2Supreme Court of the United States. About the Court – Current Members
- Stephen Johnson Field (1863–1897). Roughly 34 years and 6 months. Appointed by Abraham Lincoln during the Civil War, Field held the longevity record until Douglas broke it in 1973.3Supreme Court of the United States. Justices 1789 to Present
- John Paul Stevens (1975–2010). Nearly 35 years, with his total in days almost exactly matching Field’s. Stevens, appointed by Gerald Ford, became a reliable member of the Court’s liberal wing.3Supreme Court of the United States. Justices 1789 to Present
- John Marshall (1801–1835). 34 years, 5 months, and 11 days as Chief Justice. Marshall established judicial review and set the Court as a coequal branch. He remains the longest-serving Chief Justice by a wide margin.4Supreme Court of the United States. Frequently Asked Questions on Justices
- Hugo Black (1937–1971). About 34 years and one month. A former U.S. Senator from Alabama, Black became one of the Court’s most forceful First Amendment voices.3Supreme Court of the United States. Justices 1789 to Present
- John Marshall Harlan I (1877–1911). About 33 years and 10 months. Known as the “Great Dissenter,” Harlan is best remembered for his solo dissent in Plessy v. Ferguson, arguing the Constitution was colorblind. His grandson, John Marshall Harlan II, also served on the Court but for a much shorter period (1955–1971).5Federal Judicial Center. Harlan, John Marshall
Together these seven justices account for roughly 240 years of decision-making. Their opinions still anchor modern constitutional law, from Marshall’s foundational rulings on federal power to Douglas’s expansive reading of privacy.
Clarence Thomas and the Record Ahead
Thomas was sworn in on October 23, 1991, and he has now served longer than every justice in American history except Douglas.1Supreme Court Historical Society. Clarence Thomas Poised to Become the Second-Longest Serving Justice To overtake Douglas, he would need to remain on the bench until May 2028. His jurisprudence has consistently emphasized originalist and textualist approaches, and the length of his tenure has produced an unusually large body of concurrences and dissents that increasingly show up in majority opinions.
No other sitting justice is close. Chief Justice John Roberts, next in seniority, took office on September 29, 2005, and Justice Samuel Alito on January 31, 2006.2Supreme Court of the United States. About the Court – Current Members Both would need many more years of active service to approach even the lower end of the all-time list.
Why Service This Long Is Possible
Article III of the Constitution provides that federal judges “shall hold their Offices during good Behaviour,” which in practice means Supreme Court justices serve for life unless they choose to step down.6Congress.gov. U.S. Constitution – Article III There is no mandatory retirement age and no term limit. The framers designed the arrangement to keep the judiciary independent of political pressure.
The only involuntary removal mechanism is impeachment by the House and conviction by the Senate.7United States Courts. Judges and Judicial Administration – Journalist’s Guide No sitting Supreme Court justice has ever been removed through that process. For tenure counting, a justice’s clock starts on the day they take the oath of office, which federal law requires before they can exercise any judicial power.8Office of the Law Revision Counsel. 28 USC 453 – Oaths of Justices and Judges That oath date can fall days or weeks after Senate confirmation, and it is the date that governs the records.
Why Modern Tenures Keep Growing
From 1789 through 1970, the average justice served roughly 15 years. Since 1970, that average has climbed to about 26 years. Three forces explain the shift. Lifespans are longer. Presidents have started picking younger nominees, recognizing that a 50-year-old appointee can serve a full generation longer than one in their 60s. And justices themselves have grown more strategic about the timing of their departures.
Since 1970, only two justices have retired before age 70: Potter Stewart at 66 and David Souter at 69. Every other departure in that period came between ages 75 and 90. The oldest justice ever to serve was Oliver Wendell Holmes Jr., who was 90 when he retired in 1932.4Supreme Court of the United States. Frequently Asked Questions on Justices Younger appointments combined with later departures mean the Court’s membership now turns over far more slowly than the framers likely anticipated, and the names at the top of the all-time list are increasingly joined by modern justices rather than nineteenth-century ones.