In the interwar period Skard marked himself as an opponent of Fascism, first and foremost as a follower of the Oxford Group. When Nazi Germany invaded Norway in 1940, Skard participated in the fighting in Gudbrandsdalen. Germany won, but one of many civil 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, Harald Krabbe Schjelderup, Anatol Heintz, Odd Hassel, Ragnar Frisch, Carl Jacob Arnholm, Endre Berner and Eiliv Skard were sent to Grini concentration camp. Skard was first incarcerated at Bredtveit from 15 October to 22 November, then at Berg until 8 December, then at Grini until 5 May 1945. An exception came in the last winter, when Skard spent a month at Victoria Terrasse.