Educated in Munich and Lausanne, he received commercial training in England and in 1897 went to South Africa, where from 1901 to 1910 he was a merchant in Cape Colony. He returned to Germany and from 1911 to 1915 studied political science in Munich and at the Colonial Institute in Hamburg.

Grimm's experiences in South Africa furnished material for his literary works, the first of which, Südafrikanische Novellen, appeared in 1913. His novel Volk ohne Raum (1926; “Nation Without Space”), in which he contrasts the wide-open spaces of South Africa with Germany's cramped position in Europe, deals with the German settlers in South West Africa, their involvement in the South African War, and their determination to retain their land despite the provisions of the Treaty of Versailles. Grimm's style was influenced by the Old Icelandic sagas.