Released from the army in 1919, Émile Coornaert passed the History teacher's examination (known in France as "l'agrégation d'histoire") and worked in Alençon, Nancy, and at the Lycée Condorcet in Paris.
He received his PhD in 1930, and was named Director of Economic Historical Studies at the École pratique des hautes études where Marc Bloch took a liking to him.
Émile Coornaert was named the Chair of History at the University of São Paulo in Brazil (1934–1935), where he created a French Studies department.
Halbwachs assessed that "Coornaert is mediocre.... he has done some scholarly work on 15th century corporations... he has a strong Belgian accent, and no other characteristics.
The group, composed notably of diplomat Paul Petit, writer Marietta Martin, and Suzanne Feingold, published La France continue beginning in 1941.
La France continue was, along with L'Université libre and Témoignage chrétien, one of the rare resistance journals which denounced the situation faced by the Jewish people.
He contributed to the relaunch of the Syndicat général de l'Éducation nationale (the General Union of National Education), affiliating it with the CFTC with Marcel Reinhard, a teacher at Lycée Louis-le-Grand.
He enforced the notion of using the union as an "instrument of social transformation" which would continue the work of the Resistance through "a revolution without hatred and without violence, inspired by a spiritual conception of the world."
After the rejection of a school policy motion which he had presented, Émile Coornaert left his position as president of SGEN but continued his involvement in the life of the union.