[3] In 1905, Mounstier, as a high school student, placed second in a competitive examination to be accepted as a plebe in the U.S.
In the latter year, he was reporting from the Mexican border, and in World War I he was sent to Europe by the New York Herald.
In 1920 he returned to Europe on a commercial assignment to investigate business conditions "with special reference to the copper and brass industries.
[9] Mountsier was also the American literary agent for writer D. H. Lawrence, beginning in October 1920.
[1][10] Lawrence broke with his previous agent, J.B. Pinker, and replaced him with Mountsier in New York and Curtis Brown in London.