Made a teacher of literature in 1936, he taught until 1945, briefly as a teacher of literature in Prades, but he preferred to be a schoolteacher in Thiais in order to move closer to Paris. He then collaborated with André Breton on the review Clé, which protested against the internment in France of Spanish republicans in the early phases of the Spanish Civil War.
After a brief period of mobilization, he returned to teaching during the Nazi occupation and engaged in clandestine political activities. His resistance network (which included a German soldier who would be executed) was dismantled in the course of a raid. David Rousset and several of his other members were deported. Rousset's wife helped Nadeau to escape deportation.
This first part of his life led to the publication in 1945 of his Histoire du surréalisme (History of Surrealism) published in the United States in 1965 and the United Kingdom in 1968). The book was the major reference work on surrealism for long despite the fact that André Breton disliked it.
Simone de Beauvoir; Italo Calvino; Jose Maria Castellet; Julio Cortazar; Jean Daniel; Maurice Nadeau; et al. (6 May 1971). "An Open Letter to Fidel Castro". The New York Review. in support of Herberto Padilla, first published in Le Monde on 9 April 1971.