A colonel in the American Civil War, he dabbled in railroad investment, but was forced to yield control of the original New York Central Railroad line (from Albany to Buffalo) to Cornelius Vanderbilt. His principal business interest was of course the vast Astor Estate real estate holdings in New York City, which he managed profitably and parsimoniously.
In 1859 he built a home at 350 Fifth Avenue, which is today the street address of the Empire State Building, and later added an imposing vacation home, Beaulieu, in Newport, Rhode Island.
Aristocratic by inclination, he increasingly visited London in his later years, and his son William Waldorf Astor (1848-1919), the same year that John Jacob III died, would move there permanently with his family, dying as 1st Viscount Astor.