Achenbach was a member of the Nazi Party prior to 1945 and served in the German Embassy in Paris during World War II, where he was responsible for rounding up 2,000 Jews as hostages.

Towards this goal, in 1951, he organized a lobby group which employed Werner Best, former deputy chief of the SD, and Franz Six, one of the leaders of mobile killing units in the Soviet Union and a convicted war criminal.

After the war, Achenbach joined the Free Democratic Party, served as its foreign affairs spokesman and was elected to the Landtag of the state of North Rhine-Westphalia.

He was assisted by his contacts from his time as CEO of the Foundation Adolf Hitler Fund, including Hugo Stinnes, Jr., Heinz Wilke, Wolfgang Diewerge, etc., all of whom were former Nazis.

As an active member of the Foreign Affairs Committee in the Bundestag until 1976, he was responsible for the Franco-German Supplementary Agreement to Transition signed in 1971, and successfully prevented its ratification until 1974 when he was discredited by the campaigns of Beate and Serge Klarsfeld.