We introduce the photochemical polythiol process, in which we use ambient light to decompose bismuth, antimony, copper, and lead thiolates to metal nanoparticles. Focusing on bismuth, we produce rhombohedral nanoparticles with narrow size distributions. The approach allows a single-phase synthesis of uniform non-noble metal nanoparticles without a secondary size-selection process. It minimizes use of chemicals and solvents and is more environmentally friendly than competing processes described in the literature.