He was a disciple of Jean-Étienne Dominique Esquirol (1772–1840), and a colleague of Jean-Pierre Falret (1794–1870), with whom he founded a private mental institution at Vanves in 1822.
Voisin was a leading advocate of the phrenological theories of Franz Joseph Gall (1758–1828) and Johann Spurzheim (1776–1832), and along with Louis Delasiauve (1804–1893) and Jacques-Étienne Belhomme (1800–1880), he is considered to be one of the more prominent members in the French school of phrenology.
Voison was particularly interested in the role phrenology could be used to understand the pathology of mental retardation and insanity.
Voisin also did extensive research of satyriasis and nymphomania, and was interested in the relationship between hypersexuality and hysteria.
These classifications predated, and in a general sense are a parallel to the Freudian concepts of superego, ego and id.