Among other things, Schjelderup learned psychoanalysis. He helped persons like Otto Fenichel and Wilhelm Reich to migrate from Nazi Germany to Norway. Then, after Nazi Germany invaded Norway in 1940, Schjelderup became leader of the university's "Aksjonsutvalget", a resistance committee. Open protests ensued when the Nazi authorities were about to change the rules for admission to the university in autumn 1943. In retaliation, the authorities arrested 11 staff, 60 male students and 10 female students. The staff Johannes Andenæs, Bjørn Føyn, Johan Christian Schreiner, Eiliv Skard, Anatol Heintz, Odd Hassel, Ragnar Frisch, Carl Jacob Arnholm, Endre Berner and Harald K. Schjelderup were sent to Grini concentration camp. Schjelderup was first incarcerated at Bredtveit from 15 October to 22 November, then at Berg until 8 December, then at Grini until 5 May 1945. He also spent time at Victoria Terrasse under interrogation.