Telegraphen-Korrespondenz Bureau (since 1946 named "Austria Presse Agentur"), in 1898 Hahn became a student at the Universität Wien starting with a study of law.

After 1905/1906 as a stand-in for Otto Stolz at the University of Innsbruck and some further years as a Privatdozent in Vienna, he was nominated in 1909 Professor extraordinarius in Czernowitz, at that time a town within the empire of Austria.

He was also interested in philosophy, and was part of a discussion group concerning Mach's positivism with Otto Neurath (who had married Hahn’s sister Olga Hahn-Neurath in 1912), and Phillip Frank prior to the First World War.

After Anschluss the fact that Hans Hahn had been of partial Jewish origin[2] caused Gödel's difficulties with getting a position at the University of Vienna.

[3] Within the Vienna Circle, Hahn was also known (and controversial) for using his mathematical and philosophical work to study psychic phenomena; according to Karl Menger he sometimes openly advocated further research into extrasensory perception while lecturing.