Following the appointment of Adolf Hitler as the German Chancellor on 30 January 1933, Philipp was appointed "Oberpräsident" (Governor) of Hesse-Nassau in June 1933. With the electoral success of Hitler's political party, he also became a member of the Reichstag and of the Staatsrat of Prussia. Philipp played an important role in the consolidation of National Socialist rule in Germany. He introduced other aristocrats to NSDAP officials and, as son-in-law of the king of Italy, was a frequent go-between for Hitler and Benito Mussolini. He also acted as an art agent for Hitler in Italy. On March 11th 1938 he delivered Hitler's letter of reassurance to Mussolini prior to Hitler's marching into Austria, and received a gushing call from Hitler upon the news of Mussolini's acquiescence.