He brokered works by Caspar David Friedrich to collectors and museums, including the 1930 painting Chalk Cliffs on Rügen from the Julius Freund Collection in Berlin to the Swiss collector and patron Oskar Reinhart from Winterthur, with whom Nathan had an increasingly close business relationship and friendship.
After the Nazis came to power, Nathan had to relocate the gallery to Ottostraße 5, after which the professional ban against Jews forced him to transfer the company to his long-term employee Käthe Thäter in 1935.
[3] Thanks to the help of Oskar Reinhart and St. Gallen City Mayor Konrad Nägeli, Nathan received a work permit.
[11][12] In 1948 Nathan received Swiss citizenship, in 1951 he moved with his family to Zurich, where he continued to build up Emil Georg Bührle's private collection.
He also remained active for Oskar Reinhart, for whom he was able to negotiate several purchases from the estate of Otto Gerstenberg's collection, for example the painting Au Café by Édouard Manet.
Nathan's activities expanded in Zurich, he brokered works to museums in Switzerland, Germany, England and the USA as well as to a number of Swiss and foreign private collectors.
joined his father's art shop in 1953, Fritz Nathan remained active as a dealer until shortly before the end of his life.