Two-dimensional (2D) copper-based ternary and quaternary semiconductors are promising building blocks for the construction of efficient solution-processed photovoltaic devices at low cost. However, the facile synthesis of such 2D nanoplates with well-defined shape and uniform size remains a challenge. Reported herein is a universal template-mediated method for preparing copper-based ternary and quaternary chalcogenide nanoplates, that is, CuInS2, CuInxGa1−xS2, and Cu2ZnSnS4, by using a pre-synthesized CuS nanoplate as the starting template. The various synthesized nanoplates are monophasic with uniform thickness and lateral size. As a proof of concept, the Cu2ZnSnS4 nanoplates were immobilized on a Mo/glass substrate and used as semiconductor photoelectrode, thus showing stable photoelectrochemical response. The method is general and provides future opportunities for fabrication of cost-effective photovoltaic devices based on 2D semiconductors.