Nonnenmacher served in the German Army during World War I. He studied at the Dresden Academy of Fine Arts, and was a member of the Association of German Artists.
In 1919 he married the sculptor Erna Rosenberg (1889-1980). They lived and worked in Berlin at Potsdamer Str. 29, the former studio of Lyonel Feininger.
Before the rise of Nazism, Nonnenmacher was a well-known sculptor whose works adorned many public buildings in Germany. Hermann and Erna's art was classified as degenerate by the Nazis, and much of his public sculpture was destroyed. Erna was persecuted as a Jew and they emigrated to London in 1938.
During the second world war Hermann and Erna were interned on the Isle of Man, where Hermann made and exhibited artwork. After the war they set up a studio in a house off Archway Road, London.
Nonnenmacher's 1928 sculpture "Abschied" (Farewell) is on display in the Berlinische Galerie Berlin.