In his earlier years he showed an aptitude for mathematics, but eventually he devoted himself to the study of natural history and of medicine, and in 1824 he was appointed assistant naturalist to his father.

In 1829 he delivered for his father the second part of a course of lectures on ornithology, and during the following three years he taught zoology at the Athénée, and teratology at the École pratique.

He became successively; inspector of the academy of Paris (1840), professor of the museum on the retirement of his father (1841), inspector-general of the university (1844), a member of the royal council for public instruction (1845), and on the death of Henri Marie Ducrotay de Blainville, professor of zoology at the Faculty of Sciences (1850).

[5][6] From 1832 to 1837 he published his great teratological work, Histoire générale et particulière des anomalies de l’organisation chez l’homme et les animaux.

[7] Isidore Geoffroy Saint-Hilaire is commemorated in the scientific name of a species of turtle, Phrynops hilarii.