Mellon's father, Thomas Mellon, rose to prominence in Pittsburgh as a banker and attorney. Andrew began working at his father's bank, T. Mellon & Sons, in the early 1870s, eventually becoming the leading figure in the institution. He later renamed T. Mellon & Sons as Mellon National Bank and established another financial institution, the Union Trust Company. By the end of 1913, Mellon National Bank held more money in deposits than any other bank in Pittsburgh, and the second-largest bank in the region was controlled by Union Trust. In the course of his business career, Mellon owned or helped finance Alcoa, the New York Shipbuilding Corporation, Old Overholt whiskey, Standard Steel Car Company, Westinghouse Electric Corporation, Koppers, the Pittsburgh Coal Company, the Carborundum Company, Union Steel Company, the McClintic-Marshall Construction Company, Gulf Oil, and numerous other businesses. He was also an influential donor to the Republican Party during the Gilded Age and the Progressive Era.