There he studied under Honoré Daumet and Charles Girault,[12] and met fellow architecture student Emmanuel Louis Masqueray, who would, in 1897, join the Warren and Wetmore firm.

Warren took particular pride in his design of the new library building of the Catholic University of Leuven, which was finished in 1928.

[14] Two of the firm's major works were the construction of Grand Central Terminal and of the Biltmore Hotel, both in New York City.

[16] Charlotte was the eldest daughter of Gabriel Mead Tooker, a prominent New York lawyer and member of Mrs. Astor's famous "Four Hundred".

[17][18][19][20] Together, they are the parents of:[21] In 1927, Warren and his brother George each inherited $2,314,143 from the estate of their uncle, Lloyd Phoenix.

[15] In 1917, Warren received the Medal of Honor from the American Institute of Architects for the firm's work.