Hallgarten was a student of Max Weber in the University of Munich for a short time.
in Munich, taught by Hermann Oncken and Karl Alexander von Müller.
When World War II ended, Hallgarten returned to the US, working as a historian, initially for the U.S. Army.
He was a guest professor several times: in the U.S., in Germany, Japan (1965), India (1965) and Italy (1967), without a tenured professorship until 1972.
Then he became Robert Lee Bailey professor at the University of North Carolina in Charlotte.