Prof. dr. Pablo Mendes de Leon commenced to work for Leiden University in 1985, where he obtained his doctoral (PhD) degree (with honours) on 1992 on a thesis called "Cabotage in International Air Transport Regulation". In addition to his teaching functions, he acted as Director of the International Institute of Air and Space Law, which was formally established in 1986.

From 2003, prof dr. Mendes de Leon is Director of Air Law Research of the International Institute of Air and Space law, and lectures private international air law and competition law in the LL.M. programme of the Institute. Moreover, he is a speaker at conferences on international aviation developments.