In May 1929 he joined the National Socialist German Students' League (NSDStB) and in February 1930 the NSDAP at Hanover.
Shortly afterwards he announced the relocation of the offices to Frankfurt am Main, where all anti-Jewish 'research establishments' under Alfred Rosenberg's direction were concentrated.
In addition, Schirmer continued to be involved in Nazi cultural plunder activities for the vast Amt Rosenberg operation once World War II began.
Schirmer was Oberreichsleiter (general director) of the Netherlands Task Force (AG Niederlande; later HAG) from September 1940 until May 1941.
His replacement as editor of World-Service in September 1943 occurred after Schirmer came under suspicion of fraud because he had allegedly taken a valuable postage stamp collection seized in Paris from Jewish owners for his own private purposes rather than those of the German state.