Among his friends were Jean-Paul Sartre, Simone de Beauvoir, Gaston Bachelard and Georges Politzer.
In September 1939, he volunteered for the French Army despite suffering from a heart condition.
Mobilized as a soldier in Rethel, he began to write his Journal de guerre in January 1940 in the middle of the Phoney War.
He survived several air attacks and bombardments during the Fall of France (May–June 1940).Under the German Occupation he was a teacher in Dieppe but suffered from the first French Statute on Jews (October 1940).
He was finally excluded from teaching in July 1941.
By that time, he was already active in the French Resistance.
From 1940, he was liaison officer between Dieppe, Rouen and Paris.
Becoming part of the underground, he joined a group of communist Resistance in Rouen, where he participated in actions against the German occupiers.
Arrested in February 1942 after the sabotage of a factory, he was imprisoned and tortured.
Judged in Paris, he was condemned to death by a German military tribunal.
He refused to sign his appeal for a reprieve.
Feldman was executed by a firing squad on 27 July 1942.
Addressing the German soldiers just before the salvo, he called out to them: "Imbeciles, it is for you that I die! "His last words inspired numerous French writers : Jean-Paul Sartre and Louis Aragon were among them.