August Zehender was born at Aalen near Württemberg in a family of a railway official.
In 1918, he joined the army and attended the non-commissioned officers' school at Ellwangen. In 1920, he was posted to the 25th Schützen Regiment at Schwäbisch Gmünd. In 1935, Zehender was posted to the SS-Verfügungstruppe (his NSDAP party number was 4263133 and his SS service number 224219). He served with the III Battalion, SS-Standarte Germania at Ellwangen, where he was in charge of a platoon in the machine-gun company. Several years later, he became the commander of the 4th (machine-gun) Company in SS-Regiment Deutschland. After promotion to Sturmbannführer, he was given command of a motorcycle battalion in Panzer Division Das Reich, having as his company commanders Wilhelm von Kment, Fritz Klingenberg and Christian Tychsen.
In January 1943, Zehender's regiment took control of the village Cholomedina, fought off several counter-attacks from the enemy and made further attacks deeper into the territory held by the Soviet forces. For these actions he was promoted to Obersturmbannführer and awarded the Knights Cross on 10 March 1943.