He studied veterinary medicine at the Ecole Nationale Vétérinaire d'Alfort from 1892 to 1896, working, while a student, as an assistant to pathologist Edmond Nocard (1850–1903).

He started as a technician in charge of preparing Calmette's serum (antivenom against snake bites) and the vaccine against smallpox.

He considerably improved the production techniques of the latter by using rabbits as intermediate hosts and developed a method to quantify the remaining virulence of these vaccines.

Henceforth, he and Calmette developed ways of attenuate the pathogenic activity of Mycobacterium, using successive transferrals of culture.

In 1908, after successfully obtaining an immunologically active preparation that could be used to produce a vaccine, he published with Calmette the results of what was named the BCG.