The article explores the Islam envisioned in the extensive writings of one of the most prominent German converts to Islam in Weimar Germany, the Jewish poet, philosopher, and political activist Hugo Marcus (1880–1966). Marcus's understanding of Islam is a surprisingly Eurocentric and even Germanic one. It is not only the religion of the German past, Marcus claims, but also, given its faith in the intellect and in progress, the religion of the future. His ideas do not figure in the historiography of Weimar Germany. While many of the new political notions of the future that Weimar writers contemplated have been explored, scholars have paid less attention to the spiritual and religious utopias envisioned in the 1920s. This article engages with German responses to the rupture of World War I and the realm of imagined political possibilities in Weimar Germany by focusing on one such utopia overlooked in historiography, Marcus's German-Islamic synthesis.