Michel François joined the École Nationale des Chartes in 1927 and graduated first place in the 1931 class with a thesis entitled Histoire des comtes et du comté de Vaudémont au Moyen Âge, which earned him the Molinier prize and was published soon after by the Lorraine Archaeological Society.
Attracted to teaching, he supplied Robert Marichal from 1942 to 1945, then a POW in Germany, to the chair of language and French literature from the Middle Ages at the Institut catholique de Paris.
In 1942–1943, he provided locum for Charles Samaran in his Latin and French palaeography conference at the École pratique des hautes études.
Finally, on 1 October 1953 he succeeded Charles Perrat to the chair of history of political, administrative and judicial of France at the École des chartes.
In 1964, at the death of Alain Dain, he was elected dean of the Faculty of Arts of the Institut catholique and member of the Académie des Inscriptions et Belles-Lettres in 1969.