He was a field officer of the Waffen-SS (he had the rank of SS-Standartenführer der Waffen-SS, comparable with the rank of colonel). He was personal adjutant to the commander of the Schutzstaffel (SS), Heinrich Himmler. He held this position between November 1940 and August 1941. Peiper fought on both the Eastern Front against the Red Army and the Western Front against the Western Allies. He won the Knight's Cross of the Iron Cross with Oak Leaves and Swords for bravery on the battlefield and his leadership skills. By 1945, he was in command of a regiment of the Waffen-SS. He was the Waffen-SS's youngest regimental colonel.