Hewlett graduated from Columbia University School of Mines in 1890. During his time at Columbia, Hewlett studied architecture under William Robert Ware and was captain of the varsity football team. After a year of study at the École des Beaux-Arts in Paris, he joined the prestigious architectural firm of McKim, Mead & White, where he met his future business partner Austin W. Lord. In 1894, he and Lord founded the New York architectural firm of Lord and Hewlett. The firm designed many notable buildings and monuments.
James Monroe Hewlett was the father-in-law of Buckminster Fuller[2] and is credited with the creation of the mural of the heavens on the ceiling of Grand Central Terminal in New York City.[3] "Hewlett and Fuller founded a construction company together which used Soundex, a Celotex product in modules for house construction".[4]