Having decided to become an architect, he studied at the École des Beaux Arts, Paris, as a pupil of Charles Laisné and Léon Ginain, and was awarded the Deschaumes Prize by the Institute of France.

While in their employ, Masqueray created the watercolor elevation of the Ponce de Leon Hotel in St. Augustine, Florida.

[4] Other important work on the boards during his time with the firm included the Hotel Alcazar, St. Augustine, Florida, 1887, now the Lightner Museum, The Commonwealth Club, Richmond, Virginia, 1891, and the Edison Building, New York City, 1891 (razed).

Five years later, he joined the office of Richard Morris Hunt (1827–1895), the first American architect to attend the École des Beaux Arts; in Hunt's firm he helped design many notable buildings including the Elbridge Gerry residence in Marblehead, MA, the William Astor house on Fifth Avenue in New York City, and Ochre Court in Newport, Rhode Island.

According to contemporary published accounts of the exhibitions of the Atelier Masqueray, those who were his students include: This list is incomplete; you can help by expanding it.

[8] Work underway while Masqueray was with the firm includes: New York Yacht Club (1898), Westmorly, Harvard, MA (1898), High Tide (William Starr Miller house), 79 Ocean Avenue, Newport, Rhode Island, (1900), The Racquet House at Tuxedo Club, Tuxedo Park, NY, (1890-1900), and the Mrs. Orme Wilson residence (now the India Consulate), 3 East 64th St., New York (1900–03).

Masqueray in turn employed Louis C. Spiering (a fellow alumnus of the École des Beaux-Arts) and some of his former students including Frank Swales and George Nagle.