In 1980, he participated in collaborative efforts by Herbert A. Simon to conduct research on concepts of rationality in neoclassical economics.
[4] Beginning in the 1990s, Mongin participated in a movement in attempt to reform normative economics and lift limits on the global market.
[5] Building off of ideals from John Harsanyi on utilitarianism,[6] he clarified his economic beliefs in response to criticisms of his mentor, Amartya Sen. Mongin's research program on normative economics started at the Université catholique de Louvain, where he was a visiting professor from 1991 to 1996 and where he collaborates with Claude d'Aspremont.
After his time in Belgium, he worked in the THEMA laboratory at Cergy-Pontoise University near Paris, where he met Marc Fleurbaey and Jean-François Laslier.
[7] At the start of the 2000s, Mongin concluded much of his research and began applying his economic theories to politics and the judiciary.