[4] Theodore became an apprentice in his father's firm and later was made a partner working with his brother Henry Osborne Havemeyer.

[5] His portrait was painted by the Swiss-born American artist Adolfo Müller-Ury, one is now in the New York State Museum at Albany; Müller-Ury also painted in 1891 a huge portrait of his wife Emilie de Loosey Havemeyer (Preservation Society of Newport County, Rhode Island (at Rosecliff).

The family owned many estates including, a town house in New York City at 244 Madison Avenue (on the southwest corner of 38th Street), a "cottage" on Bellevue Avenue in Newport, Rhode Island, and 500 acres in Mahwah, New Jersey, called Mountain Side Farm.

[9] Together, they were the parents of nine children, five daughters and four sons, including: Havemeyer died intestate at his home, 244 Madison Avenue in New York City, on April 26, 1897.

His funeral service was held at St. Patrick's Cathedral in New York and he was buried at Green-Wood Cemetery.