In this study, we prepared a low-cost novel Cu/Cu₂O/BC nanocomposite visible-light photocatalyst by the impregnation method using CuSO₄·5H₂O and rice husk biochar (BC) as raw materials and Na₂S₂O₄ as a single reductant to improve the stability and dispersion of the Cu/Cu₂O nanoparticles, in order to solve their aggregation tendency during photocatalysis. The morphology and structure of the Cu/Cu₂O/BC were characterized using various analytical and spectroscopic techniques. The photocatalytic effect and cyclic stability of the synthesized photocatalyst on methyl orange (MO) removal were investigated under visible light radiation and various parameter conditions, including the mass ratio of BC to Cu/Cu₂O, initial MO concentration, pH, temperature, and catalyst dosage. The results show that the synthesized Cu/Cu₂O/BC nanocomposite composed of Cu/Cu₂O spherical particles was loaded on the BC carrier, which has better stability and dispersion. The best adsorption–photocatalytic effect of the Cu/Cu₂O/BC is exhibited when the mass ratio of BC to Cu/Cu₂O is 0.2. A total of 100 mg of Cu/Cu₂O/BC can remove 95% of the MO and 88.26% of the COD in the aqueous solution at pH = 6, T = 25 °C, and an initial MO concentration of 100 mg/L. After five cycles of degradation, the MO degradation rate in the sample can still remain at 78.41%. Both the quasi-secondary kinetic model and the Langmuir isothermal adsorption model describe the adsorption process. Additionally, the thermodynamic analysis demonstrates that the photocatalytic process follows the quasi-primary kinetic model and that the removal process is of spontaneous heat absorption. The photocatalyst described in this paper offers a cost-effective, easily prepared, and visible-light-responsive solution for water pollution treatment.