His major contribution was the popularization of the egalitarian doctrines of the French philosopher Jean-Jacques Rousseau in Japan.
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While in France, Nakae translated some of the works of Jean-Jacques Rousseau into Japanese (most importantly, Rousseau’s "Du contrat social") and Eugène Véron's L'esthétique.
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After the Meiji Restoration, he was selected as a member of the Iwakura Mission and travelled abroad (under the patronage of the Justice Ministry) to study philosophy, history, and French literature in France, where he lived from 1871 until 1874.