Hughes was elected by the House of Representatives as the President of the United States on February 1, 1921 after a hard-fought 1920 presidential election where there were no candidate that had a necessary majority of electoral votes. Hughes carried a same number of states (18) with Liberal candidate, William Gibbs McAdoo, and received 199 electoral votes with one vote margin lower than McAdoo (199–200). However, with the support from the Peace Progressives at the House, Hughes was elected President, carrying 21 states on the House.
During his administration, the United States experienced a period of widespread prosperity following the end of World War I, called the Roaring Twenties. Hughes was a staunch supporter of Britain's New Liberalism, an important leader of the progressive movement of the 20th century, and represented the moderate wing of the Republican Party. Despite his progressivism, Hughes reverted many of Roosevelt's radical progressive policies, such as the National Health Service and the Federal Insurance System.
Hughes initiated the Washington Naval Conference to limit the naval deployment among the Great Powers and avoid conflict in the Pacific in 1921. Similarly significant Kellogg–Briand Pact was also ratified in 1929. The treaty renounced the war as an instrument of national policy in their relations with one another." The treaty did not achieve its intended result, but it did provide the founding principle for international law after World War II.
During his administration, the Twentieth Amendment to the U.S. Constitution was passed. It sets a term limit for election to the office of President of the United States where a person cannot be elected president more than two terms. Previously, there were two presidents that ever been elected more than two terms (Ulysses S. Grant and Theodore Roosevelt).
After completed his second presidential term, Hughes was appointed by President Herbert Hoover as the Chief Justice of the United States on February 3, 1930. Hughes replaced William Howard Taft, a fellow Republican who also formerly been U.S. President and who, in 1910, had appointed Hughes to his first tenure on the Supreme Court. Taft and Hughes are only two person to have served as the U.S. President and the Chief Justice of the U.S. Supreme Court.