On the outbreak of the First World War Witzleben he was appointed Adjutant of the 19th Reserve Brigade. He served on the Western Front where he won the Iron Cross. In April 1917, Witzleben assumed command of a battalion in the 6th Infantry. The following year he became General Staff Officer to the 108th Infantry Division.
Witzleben remained in the army and in January 1921 was given command of the 8th Machine Gun Company. He was on the General Staff of the Wehrkries IV (1922-25), 12th Cavalry Regiment (1925-26) and Infantry Command III (1926-28). W became Chief of Staff of Wehrkries IV (1929-31) and commander of the 8th Infantry Regiment (1931-33).
In 1934 Witzleben was promoted to major general and appointed commander of Wehrkries III, replacing General Werner von Fitsch, who was named Commander in Chief of the Army.
An opponent of Adolf Hitler and his government in Nazi Germany, Witzleben joined with Erich von Manstein, Wilhelm Leeb and Gerd von Rundstedt to demand a military inquiry into the death of Kurt von Schleicher following the Night of the Long Knives. However, the Defence Minister, Werner von Blomberg, refused to allow it to take place.
Witzleben was furious when his friend, General Werner von Fitsch, was dismissed as Commander in Chief of the Army on a trumped up charge of homosexuality. He was now a staunch anti-Nazi who began considering the possibility of a military coup against Hitler. The Gestapo became aware of his criticisms of Hitler and in 1938 he was forced to take early retirement. Witzleben plotted with anti-Nazis such as Ludwig Beck, Franz Halder, Wilhelm Canaris, Hans Oster, Wolf von Helldorf, Kurt Hammerstein-Equord and Erich Hoepner and they considered the possibility of a military coup.
On the outbreak of the Second World War Witzleben was recalled to the German Army. In the invasion of France Witzleben commanded the 1st Army. His troops broke through the Maginot Line in June, 1940 and then occupied Alsace-Lorraine. As a result of this action Witzleben was promoted to the rank of field marshal.
Witzleben remained in France and after the failure of the Operation Barbarossa he once again began plotting against Adolf Hitler. The Gestapo was informed that he was once again being critical of the government and in 1942 Witzleben was called back to Germany and retired.
Witzleben spent the next two years at his country estate. He kept in touch with anti-Nazis and in 1944 became involved in the July Plot. After Claus von Stauffenberg planted the bomb the conspirators thought that Hitler had been killed and Witzleben was installed as Commander in Chief of the Armed Forces and Erich Hoepner as Commander of the Home Army.
On 21st July, 1944 Witzleben was arrested and during his trial he was humiliated by being forced to appear in court without his belt and false teeth. Erwin von Witzleben was found guilty of treason and on 8th August, 1944 was executed by being hung by piano wire from a meat hook.