He was a member of the Politburo of the Central Committee of the Socialist Unity Party of Germany, and for a short time, he was East German Minister of Materials Management.

In 1939, he was arrested in France and interned, in 1941, he was handed over to the Gestapo, and in 1942 he was sentenced by the Volksgerichtshof to eight years at hard labour in a Zuchthaus for high treason.

From 1957 to 1961, he was SED Central Committee Secretary, from 1961 to 1965 chairman of the People's Economic Council (Volkswirtschaftsrat), and from 1965 to 1968 Minister of Materials Management.

In 1989, in East Germany's dying days, Neumann went back to join the Council of Ministers and was excluded from the Politburo.

From 1992 he faced accusations of "manslaughter and bodily harm on the inter-German border" for his membership in the East German National Defence Council ("Nationaler Verteidigungsrat der DDR").