Visible-light-driven photocatalysts have shown tremendous prospects in solving the energy crisis and environmental problems, thanks to their wide spectral response and high quantum efficiency. Several strategies including the expansion of visible light response and the improvement of solar energy utilization and photocatalytic quantum efficiency via more effective separation of photogenerated carriers are the current focuses of research that direct the design and fabrication of viable photocatalysts. Herein, a series of composite photocatalysts assembled from plasmonic Cu nanoparticles (NPs) and Zn3In2S6 (ZIS) solid solutions were synthesized by means of a simple solvothermal method. In comparison with the pristine ZIS semiconductor, Cu NP loaded ZIS solid solutions showed greatly enhanced photocatalytic activity, selectivity and stability towards CO2 reduction under visible irradiation. Of note was that the optimized ZIS-Cu2 exhibited an enhanced CH4 production rate of ca. 292 μL g-1 h-1 and a selectivity of ca. 71.1%, which were among the highest numbers reported hitherto. The localized surface plasmon resonance (LSPR) effect, shown by surface Cu NPs, was believed to play a critical role in the enhanced CO2 photoreduction efficiency. More importantly, the introduction of plasmonic Cu NPs could restrain the recombination of photogenerated electron-hole pairs and promote the migration of photogenerated electrons to better participate in the photocatalytic CO2 reduction in the presence of water vapor. This work thus provides a facile means to design robust and flexible composite photocatalysts for visible-light-driven CO2 photoreduction with high efficiency.