Transferring to Infantry Regiment 58, he served with that unit until the armistice, being wounded several times and earning the Iron Cross, first and 2nd class.

In May 1923, he was promoted to police captain, but in December 1923, he was sentenced to a one-year jail term and fined 500 Reichsmarks by a French military court for his involvement in separatist actions.

[2] Winkelmann's next important career move came in November 1937 when he was posted to the Hauptamt (Main Office) of the Ordnungspolizei (Orpo) located in Berlin.

[4] During Winkelmann's tenure in Hungary, in an operation directed by Adolf Eichmann, over 437,000 Hungarian Jews were deported between May and July 1944, most all of whom perished in the Nazi extermination camp at Auschwitz.

After the Hungarian government of Miklós Horthy began negotiations to sue for peace, Winkelmann, along with Edmund Veesenmayer the German Plenipotentiary to Hungary, immediately acted to remove the Horthy regime and install the Arrow Cross puppet government on 15 October 1944.

The siege of Budapest lasted until the city's fall to the Red Army on 13 February 1945, and Winkelmann retreated into Austria where he took up the position of commander of all police on 1 March.

He was temporarily transferred to Hungary on 27 October 1945 to testify at war crimes trials of members of the Arrow Cross government.

In this document, he denied all culpability for the deportation and murder of Hungarian Jews, testifying that Eichmann did not receive orders from him, but directly from the Reich Security Main Office (RSHA) in the matter of the Final Solution.