After his graduation from
Yale University in 1910, he entered the Foreign Service in 1911. His older brother Emanuel died in 1913 of sarcoma. After postings in Berlin, Paris, and South America, he was nominated as the American ambassador to Iran in 1939. The incident caused a diplomatic rupture: all consular matters were transacted through ''
chargés d'affaires'' until 1939, at which time Dreyfus was nominated. While in Iran, Dreyfus reported on the
Anglo-Soviet invasion of Iran to the
State Department. Dreyfus also served as Minister to Iceland, both before and after it
became a republic; and Minister to Sweden after
World War II. before finally returning to Afghanistan as the
United States ambassador from 1949 to 1951, when he was succeeded by
George R. Merrell. ==Later life==