Born in Youngstown, Ohio, to a family of German descent, Hillenbrand attained a Ph.D. in 1948 from Columbia University.
During his 37-year career in the U.S. Foreign Service, he held assignments in Switzerland, Washington, D.C., Burma, India, Portuguese East Africa (now: Mozambique), Germany, France, and Hungary.
After retiring from the U.S. Foreign Service, the former Ambassador Hillenbrand served as the Director-General of the Atlantic Institute for International Affairs in Paris, France, from 1977-1982.
In 2004 Ambassador Hillenbrand participated in an oral history project that focused on his role and understanding of significant world events during his career in the U.S. Foreign Service and also considered his outlook on the future.
Audio and video recordings from this project are housed in the Richard B. Russell Library at the University of Georgia.