William J. Donovan was raised in Buffalo, educated at Miss Nardin's Private School and St. Joseph's Collegiate Institute; he attended Niagara University for two years before transferring to Columbia, where he earned his A.B. in 1905 and LL.B. in 1907.

Donovan began his legal career in Buffalo with Love & Keating. In 1912, he formed a partnership that was to become the firm of O'Brian, Hamlin, Donovan & Goodyear (dissolved 1920).

Concurrently he actively pursued a military career, becoming one of the founders of Troop I, 1st Cavalry of the New York National Guard, elected as captain in 1912. In 1915, he visited Europe for the War Relief Commission; he returned to serve on the Mexican border with Troop I, then underwent training in a number of military camps, convinced that the United States' entry into World War I was inevitable. He sailed for Europe with the Rainbow Division, one of the first to mobilize, and soon became a battalion major in the "Fighting 69th" New York Infantry (known in France as 165th). Donovan was rapidly promoted to lt. colonel, then colonel.

During World War I, he was highly decorated for his leadership and heroism, receiving the Croix de Guerre, Distinguished Service Cross, the Legion of Honor medal and the Italian War Cross. After being discharged in May 1919, he sailed for Asia to investigate the White Russian government of Aleksandr Kolchak in Siberia, who was then struggling against the Bolsheviks.

In 1922, Donovan ran unsuccessfully for lt. governor of New York; in 1932 he was defeated in his bid for New York's governorship. President Harding appointed him U.S. attorney for the western district of New York in 1922; he met with considerable success prosecuting major crime rings until 1924.

Donovan resumed his law practice in Buffalo until special duties during World War II forced him to abandon it. Franklin Roosevelt assigned him to coordinate information for the Joint Chiefs, and promoted him to brigadier general and later to major general.

Donovan was also instrumental in helping to establish the Office of Strategic Services, later the Central Intelligence Agency.