Born in Vălenii de Munte, where he attended primary school, Stamatu went on to military high school and then the literature and philosophy faculty of Bucharest University. From 1936 to 1937, he was a substitute teacher at Bucharest's Cantemir Vodă High School. He was an editor at "Enciclopedia României" from 1938 to 1940. A member of the Iron Guard, he took part in the Legionnaires' rebellion. In 1941, in the aftermath of the rebellion, he left for Germany through Bulgaria, and was interned at Buchenwald concentration camp from 1942 to 1944. He was sentenced to death "in absentia" by a Romanian military tribunal. From 1945, he lived in Freiburg im Breisgau, where he studied philosophy with Max Müller at the University of Freiburg. Within that institution, he lectured on the Romanian language from 1946 to 1948 in Hugo Friedrich's department.