Thurman Wesley Arnold (June 2, 1891 – November 7, 1969) was an American lawyer best known for his trust-busting campaign as Assistant Attorney General in charge of the Antitrust Division in President Franklin D. Roosevelt's Department of Justice from 1938 to 1943.

Before coming to Washington in 1938, Arnold was the mayor of Laramie, Wyoming and a professor at Yale Law School, where he took part in the legal realism movement and published two books: The Symbols of Government (1935) and The Folklore of Capitalism (1937).

[1] Arnold served in World War I, rising to the rank of lieutenant in the United States Army (Field Artillery) and worked briefly in Chicago, Illinois before returning to Laramie, where he was a member of the Wyoming House of Representatives in 1921 and then mayor from 1923 to 1924.

As chief competition lawyer for the United States Government, Arnold launched numerous studies to support the antitrust efforts in the late 1930s.

[3] The Roosevelt administration later de-emphasized antitrust enforcement, for the stated purpose of allowing corporations to concentrate on contributing to victory in World War II.

[3] Arnold was nominated by President Franklin D. Roosevelt on February 11, 1943, to an Associate Justice seat on the United States Court of Appeals for the District of Columbia (now the United States Court of Appeals for the District of Columbia Circuit) vacated by Associate Justice Wiley Blount Rutledge.