A militant opponent of fascism and a Holocaust survivor of partial Jewish heritage, Oliva-Hagen was active in the German resistance to Nazism.
In 1941 he was arrested by the police during an illegal leaflet campaign and imprisoned in the Moabit prison, where he was subjected to Nazi human experimentation.
[citation needed] Hagen's father, Hermann, was murdered in the special campaign against Jews on 27 and 28 May 1942, an act of revenge by the Nazis after the assassination attempt on Reinhard Heydrich.
Along with 500 other German Jews selected arbitrarily, Hagen was abducted from Berlin and taken to the Sachsenhausen concentration camp where he was murdered on 29 May 1942.
[citation needed] Following the end of World War II, Hans Oliva-Hagen lived in East Berlin when it was administered by the Soviet Union, and joined the Socialist Unity Party of Germany.