He worked at the Hôpital des Enfants-Malades, and for most of his career was associated with the Pasteur Institute in Paris.
Chaillou is best known for his development of the anti-diphtheria serum with Émile Roux and Louis Martin (1864-1946) at the Pasteur Institute.
The three men presented their findings at the Tenth International Congress of Hygiene in Budapest (1894).
From 1895 until 1914 he was chief of anti-rabies services at the Pasteur Institute.
As a medical officer during World War I he was killed on the battlefield of Vauquois.