As a student in Vienna, he was briefly kept in custody by the Nazis in 1938 because of his opposition against the annexation of Austria into Greater Germany. Later he moved to Frankfurt to study law, but he was recruited by the Wehrmacht in 1942. After spending several years in a Soviet prison, he returned to Germany in 1949 and started a career as a commentator. His wife was the Austrian journalist and author Thea Leitner.
At first, he focused on legal and sociological topics, but later he took medical and psychology-related subjects as his theme. His book So lernt man lernen (How to learn to learn), a practical manual on the psychology of learning, became a bestseller. In this often-cited book he described his Leitner System for learning by spaced repetition.