He then attended Christ Church at the University of Oxford in England where he specialized in historical studies, following which he returned to Harvard to earn an M.A.
[1] Moriarty went to work for the U. S. State Department in the foreign service, and served in consular and secretarial roles in Fiume, Italy; Mexico City; and Guatemala.
He practiced law in Providence, Rhode Island and Boston, Massachusetts for over a decade, which time also included a year in the U.S. Army at the end of World War I when he was a captain in military intelligence.
[1] Making his first contribution to the New England Historical and Genealogical Register in 1912, Moriarty submitted 134 articles to that journal over the next 54 years, most of them dealing with English feudal families.
He also contributed to more than a dozen other American and English journals, as well as writing genealogical notes in the Boston Evening Transcript for a period of 30 years.