Maršálek was arrested for being a communist in 1941 and sent to the Mauthausen concentration camp in 1942. He was made a prisoner functionary and assigned to the camp’s typing pool. Maršálek was involved in the resistance as part of the prisoners’ underground organisation. In the decades after 1945, he researched the history of the Mauthausen concentration camp and was the director of the Mauthausen Memorial.