In his early adult years, Astor returned to the United States and went to Columbia Law School, graduating with a LL.B.

They had five children:[5] After some time practising law, Astor thought he had found his true calling and an opportunity to make a name for himself outside of his family's fortune by entering the political realm.

In 1877, with his eyes set on the United States Congress, Astor entered New York City politics as a Republican.

[7] Astor was likely supported by the boss of the New York State Republican machine, Roscoe Conkling, with whom his family was involved.

Upon the death of his father in February 1890, Astor inherited a personal fortune that made him the second richest man in America.

At 13 stories high, it overshadowed the adjacent mansion of his aunt, the socialite Caroline "Lina" Schermerhorn Astor.

In 1895, he built a gothic mansion on London's Victoria Embankment at Two Temple Place overlooking the River Thames.

He commissioned architect John Loughborough Pearson to design a $1.5 million building, a "crenellated Tudor stronghold"[11] which he used as an office for managing his extensive holdings.

In 1912 he sold the Magazine, and in 1914 made a present of the Gazette and The Observer, with the building in Newton Street and its contents, to his son Waldorf Astor.

Astor invested a great deal of time and money in restoring the castle, building what is known as the "Tudor Village", and creating a lake and lavish gardens.

[17] In 1906, he gave his eldest son Waldorf Astor and his new daughter-in-law, Nancy Witcher Langhorne, the Cliveden estate as well as the Sancy diamond as wedding presents.

[3] In recognition of his work for charity, on 1 January 1916, he was offered and accepted a peerage of the United Kingdom under the title of Baron Astor.

[19][20] His ashes were buried under the marble floor of the Astor family chapel (also called the Octagon Temple) at Cliveden.