Under the Nazi German occupation of Poland Newerly was a member of the Polish resistance. He helped Janusz Korczak at his Orphanage and saved his diary of martyrdom. He also hid from Nazi persecution several of his Jewish colleagues from "Nasz Przegląd" daily – among them Kuba Hersztein – and transported Lejzor Czarnobroda to Warsaw after he escaped from the train to Treblinka and broke his leg. Newerly was arrested at the beginning of 1943 by the German Gestapo and imprisoned at Pawiak in Warsaw. Until the end of the war he was an inmate of Nazi concentration camps: Majdanek, Auschwitz, Oranienburg and Bergen Belsen where he was liberated.