Born in Dvinsk, Latvia, Siegel emigrated to the United States in 1905 with his parents, Mendel and Sarah (Einhorn) Siegel. The family settled in Baltimore, Maryland, where Siegel attended Baltimore City College and joined the speech and debate team now referred to as the Bancroft/Carrollton-Wight Literary Societies. He contributed to the senior publication The Green Bag and graduated in 1919. In 1922, together with V.F. Calverton [George Goetz], he co-founded The Modern Quarterly, a magazine in which his earliest essays appeared, including "The Scientific Criticism" (Vol. I, No. 1, March 1923) and "The Equality of Man" (Vol. I, No. 3, December 1923).