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.
Manfred Dörr. "Die Träger der Nahkampfspange in Gold, Heer-Luftwaffe-Waffen-SS 1943–1945". ISBN 3-7648-2585-5
Fellgiebel, Walther-Peer (2000). Die Träger des Ritterkreuzes des Eisernen Kreuzes 1939–1945 – Die Inhaber der höchsten Auszeichnung des Zweiten Weltkrieges aller Wehrmachtsteile [The Bearers of the Knight's Cross of the Iron Cross 1939–1945 — The Owners of the Highest Award of the Second World War of all Wehrmacht Branches] (in German). Friedberg, Germany: Podzun-Pallas. ISBN978-3-7909-0284-6.
Landwehr, Richard (1999). Steadfast Hussars : the last cavalry divisions of the Waffen-SS. Brookings, Ore.: Siegrunen. ISBN 1-57638-130-7.
Scherzer, Veit (2007). Die Ritterkreuzträger 1939–1945 Die Inhaber des Ritterkreuzes des Eisernen Kreuzes 1939 von Heer, Luftwaffe, Kriegsmarine, Waffen-SS, Volkssturm sowie mit Deutschland verbündeter Streitkräfte nach den Unterlagen des Bundesarchives [The Knight's Cross Bearers 1939–1945 The Holders of the Knight's Cross of the Iron Cross 1939 by Army, Air Force, Navy, Waffen-SS, Volkssturm and Allied Forces with Germany According to the Documents of the Federal Archives] (in German). Jena, Germany: Scherzers Miltaer-Verlag. ISBN978-3-938845-17-2.
Thomas, Franz (1998). Die Eichenlaubträger 1939–1945 Band 2: L–Z [The Oak Leaves Bearers 1939–1945 Volume 2: L–Z] (in German). Osnabrück, Germany: Biblio-Verlag. ISBN978-3-7648-2300-9.