William O. Douglas served the longest on the U.S. Supreme Court, with a tenure of 36 years and 209 days as an associate justice from 1939 to 1975.

Quick Scoop

  • The justice with the longest service in Supreme Court history is William O. Douglas.
  • He was appointed by President Franklin D. Roosevelt and served from April 17, 1939, until November 12, 1975.
  • His time on the bench totaled 13,358 days, a record that no other justice has yet surpassed.

Why Douglas Stands Out

  • Douglas served through World War II, the Cold War, and the civil rights era, shaping major decisions on civil liberties and environmental issues.
  • Even today, discussions about long-serving justices often use Douglas as the benchmark for “how long a justice can realistically stay on the Court.”

Context With Other Long-Serving Justices

  • Other notably long-serving justices include Stephen J. Field, John Paul Stevens, and Chief Justice John Marshall, but all fell short of Douglas’s record.
  • Current justice Clarence Thomas is among the longest-serving in history and is projected to approach Douglas’s mark if he remains on the Court for several more years.

TL;DR: If you’re asking “which Supreme Court justice served the longest,” the answer is William O. Douglas, with more than 36 years on the bench.

Information gathered from public forums or data available on the internet and portrayed here.