Mo_ₓMn_₁₋ₓFe_₂O_₄/g C_₃N_₄ nanocomposites were successfully synthesized via the hydrothermal method by incorporating mixed spinel ferrite (Mo_ₓMn_₁₋ₓFe_₂O_₄) nanoparticles onto graphitic carbon nitride (g C₃N₄) sheets to enhance visible light-driven photocatalytic performance. XRD, SEM, TEM, FT-IR, and UV-Vis were used to characterize the synthesized nanocomposites, and the successful formation of the heterostructure with an enhanced surface area and modified bandgap was observed. The Mo_ₓMn_₁₋ₓFe_₂O_₄/g C_₃N_₄ catalysts effectively showed improved photocatalytic degradation of Direct Green 6 (DG 6) dye under visible light irradiation, which is superior to g C_₃N_₄ and ferrite. The performance of the composite is enhanced due to the synergistic effect between Mo_ₓMn_₁₋ₓFe_₂O_₄ and g-C_₃N_₄ parts, where efficient separation of electron hole pairs and long light absorption take place. The degradation reaction of DG 6 was found to be of pseudo-first order, and the radical trapping experiments suggested that the major reactive oxygen species in the photocatalytic reaction were the superoxide radicals (•O_₂^⁻). The results show the potential of Mo_ₓMn_₁₋ₓFe_₂O_₄/g-C_₃N_₄ nanocomposites as an efficient visible light photocatalyst working for wastewater treatment applications.