[2] Neumann began a legal clerkship in January 1918 with the Prussian state judicial administration in Stettin (today, Szczecin).

After passing his second state legal examination in October 1920, he entered the civil service as a government attorney (Regierungsassessor) in the Prussian Ministry of the Interior and, thereafter, in its Essen district office.

In the summers of 1935 through 1937, he participated in military training exercises with the Reiter Regiment 9, headquartered in Fürstenwalde, and later advanced to the rank of Rittmeister of reserves.

[1] On 23 October 1936, Neumann was appointed the director of the Foreign Currency Department of the Office of the Plenipotentiary for the Four Year Plan, headed by Göring.

After the occupation of Czechoslovakia in March 1939, Neumann was involved in the actions that resulted in the takeover of the Petschek coal concern by the Reichswerke Hermann Göring conglomerate.

He also profited personally from the Aryanization process, as he lived in a villa near the Berlin Botanical Garden that a Jewish woman had been forced to sell in order to emigrate.

His objection was not that they should be spared based on humanitarian or moral grounds, only that they not be deported before replacements could be found, thus temporarily retaining them for their economic benefit to the Reich.

On 1 August 1942, Neumann left government service at his own request to become the General Director of the German Potassium Syndicate (Deutsches Kalisyndikat [de]) where he remained through the fall of the Nazi regime in May 1945.