Coleman enrolled at Columbia University in New York City, from which he graduated in 1909. After graduation, he worked as a journalist, first taking a position with the "New York Sun." During the course of his work as a New York journalist, Coleman covered the New York garment workers strike of 1909–1910 as well as the catastrophic Triangle Shirtwaist Factory fire of 1912. These experiences had a radicalizing effect and not long after the Triangle fire he joined the Socialist Party of America (SPA) and — while still working for the "Sun" — Coleman began contributing articles to the SPA's New York daily newspaper, the "New York Call."