Born in Mühlheim am Main in the German Empire, Weissenberger, who had been a glider pilot in his youth, volunteered for service in the Luftwaffe of Nazi Germany in 1936. Following flight training, he was posted to the heavy fighter squadron of Jagdgeschwader 77 (JG 77—77th Fighter Wing) in 1941. He claimed his first aerial victory over Norway on 24 October 1941.