Born near Marietta, Georgia, on October 31, 1863, William McAdoo attended the University of Tennessee without graduating. Admitted to the bar in 1885, he practiced law in Chattanooga before moving to New York City in 1892, where he became president of the Hudson and Manhattan Railroad Company, which opened the first tunnels under the Hudson River between New York and 591:New Jersey]. He was a Democrat and figured prominently in Woodrow Wilson's 1912 campaign for the presidency. He married one of Wilson's daughters.
McAdoo became Wilson's secretary of the treasury in 1913 and supervised the establishment of the Federal Reserve System after passage of the Federal Reserve Act in that year. After American entry into World War I, McAdoo directed the Liberty Bond campaigns and the program of war loans to the Allies. As director general of railroads from 1917 to 1919, he managed the entire railroad network of the United States.
McAdoo actively sought the presidential nomination in 1924. Supported by the rural, Protestant, prohibitionist wing of the party, his opponent was Alfred E. Smith, who was the favorite of the urban, Catholic, "wet" Democrats. The contest at the convention was finally broken on the 103rd ballot when John W. Davis was nominated as the "dark horse" candidate.
At the 1932 convention, McAdoo used his influence to help Franklin D. Roosevelt gain the nomination. Elected a senator from California in 1932, he supported the New Deal. He lost his bid for reelection in 1938 and died in Washington, D.C. on February 1, 1941.