Educated at Hurstpierpoint College, Austen-Smith joined the Royal Air Force in 1943 during the Second World War. After serving with Number. 33 Squadron Royal Air Force in Malaya in the early 1950s, he became Officer Commanding Number.
73 Squadron Royal Air Force in 1956 and Officer Commanding Number.
57 Squadron Royal Air Force in 1964. He went on to be Station Commander at Royal Air Force Wattisham in 1968, Commandant of the Royal Air Force College Cranwell in 1972 and Senior Air Staff Officer at Headquarters Near East Air Force in 1975.
After that he became Commander of British Forces Cyprus and Administrator of the Sovereign Base Areas in 1976 and Head of the British Defence Staff in Washington, District of Columbia in 1978 before retiring in 1981. In retirement Austen-Smith served as a Gentlemen Usher to the Queen.