After attending the gymnasium (a form of high school) in Esslingen, he studied political science and sociology at the Universities of Tübingen, Berlin, and Heidelberg, and in 1923 gained a doctorate.

On 6 October Friedrich Möllhausen sent a message to Ribbentrop, reporting that Obersturmbannführer Herbert Kappler of the SS had been ordered to arrest the Jews of the city and take them to Upper Italy, "where they are to be liquidated", and that the commandant of Rome, General Stahel, was opposed to this.

Ribbentrop visited Hitler at the Wolf's Lair and later ordered that Rahn and Möllhausen be informed "that by a Führer Directive the 8,000 Jews living in Rome are to be taken to Mauthausen, Upper Danube, as hostages".

[5] On 9 October 1944, Admiral Miklós Horthy, Regent of Hungary, a German ally, announced the conclusion of a separate peace with the Soviets.

On 7 June 1949 he was classified as denazified in Class V (exonerated), especially in view of his argument that through diplomatic channels he had saved about 1,800 people who had been taken prisoner by the Gestapo in North Africa.

[1][2] In 1960 Rahn attended Der Stahlhelm funeral at Bad Wiessee of Generalfeldmarschall Albert Kesselring, with Franz von Papen, Grossadmiral Karl Dönitz, Ferdinand Schörner, Otto Remer, Siegfried Westphal, and Josef Kammhuber, former SS officers Sepp Dietrich and Joachim Peiper.