Lieber was among the co-founders of Freie Universität.
He studied philosophy, sociology, and history in Berlin from 1942 to 1945, earning a doctorate in 1945 under the supervision of Eduard Spranger. From 1945 to 1948, he was an assistant in the Department of Philosophy at Universität Unter den Linden.
In the fall of 1948, Lieber became a research assistant within the Department of Philosophy at Freie Universität. From 1955 to 1972, he worked as a professor of philosophy and sociology (starting in 1955 as an associate professor, named a full professor on September 1, 1962). Lieber left Freie Universität in 1972 to take a position as a full professor of philosophy at the German Sport University in Cologne, where he also served as rector from 1974 to 1982.