When the national banking system was created in 1863, Baker joined with several New York stockbrokers to establish the First National Bank of New York City. Beginning as a teller and small stockholder, he was the active head of the bank by the age of 25. By 1909, when he became chairman of the board, he ranked with J.P. Morgan and James Stillman as a force in American finance and served as director of many corporations. In addition to his gift of $6 million to Harvard, he made large gifts to other institutions, including New York City's Metropolitan Museum of Art and the American Red Cross.