Well-known for having created the famous Metric Scale of Intelligence along with the psychologist Alfred Binet (1857-1911), what is less known is that Théodore Simon (1873-1961) was also a major actor of the professionalization of psychiatric nurses in France. From his engaged textbook published in 1911 to his journal, explicitly titled “L’Infirmier Psychiatrique,” which he created in 1953 via the specialized school he founded and directed between 1946 and 1957 at the Maison Blanche hospital in Neuilly-sur-Marne, Simon worked throughout his career for the acknowledgment and the training of those he considered as true partners. This is what we want to demonstrate in this paper, which redraws the forgotten career history of this militant psychiatrist in order to shine a light on his commitment to the professionalization of psychiatric nurses.