Hogan was born to Maurice Hogan and Mary E. (McSweeney) Hogan in Brooklyn, New York, on January 12, 1877. His father died when Hogan was five years old, leaving his mother to support three children on a
seamstress's wages. In the 1880s, the family moved to
Charleston, South Carolina, where they lived with Mary's sister. Hogan grew up in a household run by two widowed women, along with his cousin
James F. Byrnes, who went on to become
United States Secretary of State and governor of South Carolina. At 12, Hogan left school to work as a stockboy in a local store. A
stenographer taught him how to write in
shorthand, a skill that proved to be valuable throughout his career. He became a stenographer himself and then worked as a railway clerk, a brokerage clerk, and a reporter for a local newspaper. In his spare time, he schooled himself by reading books recommended by friends. In 1898, he joined the US Army and put his clerical and railway experience to work in
logistics, serving as secretary to the Chief Quartermaster of the Army, secretary to the Quartermaster General in Washington, and secretary to the Chief of Staff of the Army. After work, he would spend his evenings studying law at
Georgetown University. He completed the three-year program in two years, graduating at the head of his class in 1902. == Law career ==