After receiving a doctorate in philosophy from Fordham University, in 1920 Furlong became a professor of history at Cathedral College and eventually dean and president from 1938 to 1941.
At its completion in 1941 Furlong became the first principal of Cardinal Hayes High School in the Bronx until 1945 and served as secretary of education for the New York archdiocese.
Furlong was national Catholic chaplain of the Civil Air Patrol and a member of the Naval Aviation Cadet Selection Board from 1942 to 1945.
With this experience, on December 3, 1955, Furlong was appointed Auxiliary Bishop to the US Military Vicariate, a responsibility at the time of the archbishop of New York.
Cardinal Francis Spellman, Archbishop of New York, consecrated Furlong bishop on January 25, 1956.