In this study, we prepared triangular silver nanoplate/cuprous oxide (TAgNPT/Cu2O) composites with various Ag loadings to be used as photocatalysts in the photocatalytic reduction of CO2 under visible light irradiation. The microstructures, compositions, and properties of the as-prepared photocatalyst samples were characterized using various techniques. Among the as-prepared samples, 0.1 wt% TAgNPT/Cu2O exhibited the highest photocatalytic activity for reducing CO2 under visible light irradiation (green and blue light-emitting diode). The cumulative yields of methane and carbon monoxide reached 30.9 and 31.02 μmol g−1 (quantum yield of 0.32 %) under green light irradiation (wavelength = 427–622 nm), whereas the cumulative yield of methane was 19.56 μmol g−1 (quantum yield of 0.21 %) under blue light irradiation (wavelength = 412–505 nm). Finally, we proposed a possible mechanism for the enhanced catalytic performance of TAgNPT/Cu2O in CO2 photoreduction reactions.