After completing his degree, he pursued a career in academia in cities including Vienna, Oxford and The Hague.
Giorgio Gaja was appointed as the Professor in International Law at the University of Camerino in 1972.
In 1974, he was made full professor of international law at the University of Florence.
Since 1989, he has been the editor in chief of the Rivista di Diritto Internazionale, one of the most prestigious periodicals on international law in Italy.
Giorgio Gaja was appointed as counsel to the Italian Government in the ELSI case before the International Court of Justice.