R. Horace Gallatin was born in New York City on 31 December 1871 to Frederick Gallatin and his wife, née Almy Goelet Gerry. R. Horace was the great-grandson of Albert Gallatin, Secretary of the Treasury from 1802-1814. His maternal great-great grandfather was Elbridge Gerry, a signer of the Declaration of Independence. Gallatin studied law at New York Law School and was admitted to the bar in 1900, but did not practice law as a profession. He was at various times in his life a Trustee of New York Hospital, Trustee, Treasurer, and Vice President of the New York Historical Society, Director of the Cruikshank Company and Director of the 890 Broadway Company. Gallatin was a member of various New York clubs, including the Knickerbocker, Tuxedo, and Regency clubs. He married Emily Lorillard Morris on 28 April 1896. Mrs. Gallatin died on 6 November 1944; they had no children. When Gallatin died on 1 November 1948, he left his entire art collection to the National Gallery of Art in Washington.