Heterobimetallic Group 11/13 sulfide nanoparticles (AgInS2, CuInS2, Ag9GaS6, and CuGaS2) are formed by treatment of [M(S2CAr)3] (M=Ga or In) with either AgNO3 or CuCl under mild conditions. The intermediary gallium or indium tris(aryldithioate) complexes are easily prepared by stirring the appropriate metal and aryldithioc acid at room temperature. Overall, this two‐step process is a simple solution‐based method for transforming Ga and In metal into valuable ternary metallosulfide nanoparticles at relatively low temperatures.