After his father's death, Astor inherited a significant portion of the Astor fortune, including valuable real estate holdings in New York City. He actively managed and expanded these holdings, demonstrating an astute understanding of the real estate market.

Astor's ambitious project, the Astoria Hotel, was completed. This marked a significant venture into the hospitality industry. He wanted to rival his cousin William Waldorf Astor's Waldorf Hotel, this rivalry eventually lead to them joining the two hotels together.

Astor oversaw the construction of the St. Regis Hotel, a luxury hotel that further solidified his reputation as a leading figure in the hospitality industry. The St. Regis set new standards for luxury and service, attracting a wealthy and discerning clientele.

Astor continued to develop and manage various real estate properties in New York City, contributing to the city's growth and skyline. His investments played a crucial role in shaping the city's urban landscape.

Beyond real estate, Astor held patents for inventions, including a bicycle brake and a marine turbine engine. These ventures showcased his inventive mind and his desire to contribute to technological advancements.