Ya kammala karatunsa daga École normale supérieure a 1977 (a wannan shekarar kamar yadda Jean-Christophe Yoccoz, wani Fields Medalist). Ƙin karɓar haɗin kai a cikin lissafi, ya zaɓi ya gudanar da bincike a cikin ilimin lissafi kuma ya sami digirin digirgir daga Jami'ar Pierre da Marie Curie a shekarar 1979. Lions ya sami lambar yabo ta Fields, don aikinsa a kan ka'idar ƙididdigar rabuwa na rabuwa, a cikin 1994 yayin da yake aiki a Jami'ar Paris-Dauphine. Shi ne na farko da ya ba da cikakkiyar bayani ga daidaitattun Boltzmann tare da tabbaci. Sauran lambobin yabo sun haɗa da lambar yabo ta IBM a 1987 da Philip Morris Prize a 1991.
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