John Hessin Clarke (September 18, 1857 – March 22, 1945) was an American lawyer and judge who served as an associate justice of the Supreme Court of the United States from 1916 to 1922.

Clarke attempted to parlay this into a second run for a United States Senate seat early in 1914, but he faced opposition in the primary from Ohio Attorney General Timothy S. Hogan and by the spring appeared to be in danger of losing the race.

[6] In June 1916, a vacancy arose on the Supreme Court when Associate Justice Charles Evans Hughes resigned to accept the Republican nomination for President.

He also demonstrated his opposition to monopoly in United States v. Reading Company, in a ruling that became a prominent part of anti-trust law.

Apart from his dissatisfaction with his work as a justice and his ongoing difficulties with McReynolds, Clarke had recently suffered the loss of his sisters Ida and Alice.

Moreover, having witnessed the physical decline of Chief Justice Edward Douglass White, he wished to avoid a similar deterioration while on the bench.

"[14] In an interview three days after submitting his resignation, Clarke outlined a new cause he wanted to pursue – convincing Americans that the United States should join the League of Nations.

At the time, prospects for League entry were at a low ebb, its proponents having suffered the dual setback of the Senate's rejection of the Versailles Treaty and the election of the anti-League Republican Warren G. Harding as president in 1920.

Clarke's public pronouncements gave their cause a new life, and in October 1922 he became the president of a new organization, the League of Nations Non-Partisan Association.

Addressing this required a far different level of commitment than Clarke expected to make, forcing him and the rest of the Association leadership to scale back on their goals.

Focusing on the issue of entry into the World Court, Clarke continued to campaign for American involvement in international organizations and agreements for the remainder of the decade.

In 1932, he backed a clandestine effort to nominate Newton Baker as the Democratic presidential candidate, though after its failure Clarke became a supporter of the New Deal and President Franklin D. Roosevelt.

Despite misgivings about the methods, he sympathized with the goals underlying the president's Supreme Court "packing" plan, and at Roosevelt's request Clarke made a radio broadcast in March 1937 in which he defended the constitutionality of the proposal.

He was later honored by his alma mater by having a residence hall, Clarke Tower, named after him on the Case Western Reserve campus.