Karl Mousel was born on 8 December 1924 in Esch-sur-Alzette and lived in Schifflange. He joined the Wehrmacht voluntarily in June 1942 and was assigned to the Waffen-SS. He was killed in action on 18 April 1944 in Ternopil, Ukraine. During his post-war trial as a voluntary enlistee, the Luxembourgish court considered that his family supported Nazism and that he had joined the military for ideological reasons. His brother also voluntarily enlisted in the Wehrmacht in 1943.