The Sherman Antitrust Act of 1890 was initially enforced by the United States attorneys and the Attorney General. During the administration of President Theodore Roosevelt, Attorney General Philander Knox secured from Congress the first appropriation earmarked for antitrust enforcement, which funded a new position created by Congress with the title Assistant to the Attorney General. William A. Day became the first to hold this title, and took charge of antitrust enforcement, on March 17, 1903.
The Assistant to the Attorney General handled antitrust matters for three decades. On October 15, 1914, the Clayton Act was enacted. Attorney General A. Mitchell Palmer, during the administration of President Woodrow Wilson, organized the Department of Justice into divisions, creating the Antitrust Division in 1919.
The duties assigned to the Assistant to the Attorney General were changed during the administration of President Franklin D. Roosevelt by Attorney General Homer S. Cummings. On June 14, 1933, Harold M. Stephens became the first Assistant Attorney General in charge of the Antitrust Division.