In 1912, Schmitt joined the Imperial Schutztruppe and was posted to the colony of German Southwest Africa (later Namibia).

In 1919 Schmitt joined a right-wing militia known as Freikorps Eulenburg, which fought against Russian forces during the Soviet Baltic offensive of 1918–1919 and put down an uprising by ethnic Poles in Upper Silesia.

After the victory of Israeli forces in the war of 1948, the Arab League recruited Schmitt to train a pan-Arab army.

His campaign material used controversial images of Schmitt in his Wehrmacht uniform (which featured swastikas on the cap badge and Knight's Cross).

Schmitt criticised the use of the Knight's Cross in a 1967 film adaption of Gunther Grass's novel Katz und Maus ("Cat and Mouse").

The film had a high profile in Germany, due partly to it featuring acting performances by two sons of German Vice-Chancellor Willy Brandt.