<P> A total of 113 people have served on the Supreme Court of the United States , the highest judicial body in the United States , since it was established in 1789 . Supreme Court justices have life tenure , and so they serve until they die , resign or retire , or are impeached and removed from office . For the 105 non-incumbent justices , the average length of service was 6,203 days ( 16 years , 359 days ) . Their length of service ranges from William O. Douglas 's 13,358 days ( 7004133580000000000 ♠ 36 years , 209 days ) on the Court to the 163 - day tenure of Thomas Johnson . Among the current members of the Court , Associate Justice Clarence Thomas is the longest - serving justice , with a tenure of 7003980700000000000 ♠ 9,807 days ( 7003980700000000000 ♠ 26 years , 310 days ) as of August 29 , 2018 . </P>
<P> A total of 113 people have served on the Supreme Court of the United States , the highest judicial body in the United States , since it was established in 1789 . Supreme Court justices have life tenure , and so they serve until they die , resign or retire , or are impeached and removed from office . For the 105 non-incumbent justices , the average length of service was 6,203 days ( 16 years , 359 days ) . Their length of service ranges from William O. Douglas 's 13,358 days ( 7004133580000000000 ♠ 36 years , 209 days ) on the Court to the 163 - day tenure of Thomas Johnson . Among the current members of the Court , Associate Justice Clarence Thomas is the longest - serving justice , with a tenure of 7003980700000000000 ♠ 9,807 days ( 7003980700000000000 ♠ 26 years , 310 days ) as of August 29 , 2018 . </P>
who is the longest sitting supreme court justice
who is the longest sitting supreme court justice
William O. Douglas
William O. Douglas