ABSTRACT: In this study, a tertiary composite of graphitic carbon nitride (GCN) with copper and manganese is utilized for photocatalytic degradation to add to efforts for tackling environmental pollution problems. The photocatalytic efficiency of GCN is enhanced with the doping of copper and manganese. This composite is prepared using melamine thermal self-condensation. The formation and characteristics of the composite Cu−Mn-doped GCN are affirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet (UV), and Fourier transform infrared spectroscopy (FTIR). This composite has been used for the degradation of an organic dye (methylene blue (MB)) from water at neutral conditions (pH = 7) of the solution. The percentage photocatalytic degradation of MB by Cu−Mn-doped GCN is higher than that of Cu−GCN and GCN. The prepared composite enhances the degradation of methylene blue (MB) from 5 to 98% under sunlight. The photocatalytic degradation is enhanced owing to the reduction of hole−electron recombination in GCN, enhanced surface area, and extended sunlight utilization by the doped Cu and Mn.