This article reports a novel ternary nanocomposite consisting of ZnO, g-C3N4, and graphene oxide (GO) that provides enhanced photocatalytic performance and stability. The ZnO nanospheres disperse evenly and embed themselves in the porous g-C3N4. Composites with various g-C3N4 and GO to ZnO weight ratios were synthesized and characterized systematically. The results indicated that the absorption of binary g-C3N4/ZnO nanocomposites shifted to a lower energy compared to pure ZnO in a fashion consistent with the loading content of g-C3N4. Notably, the loading content of GO in the ZnO-g-C3N4 composite resulted in increased absorption in the visible range and improved charge separation efficiency, thereby drastically improving photocatalytic activity. Successful hybridization of ternary nanocomposite was confirmed by drastic quenching of fluorescence and broader visible light absorption. The optimal content of g-C3N4 in the ZnO-g-C3N4 composite was 50%, which exhibited the effective hybridization between ZnO and g-C3N4, and high photocatalytic efficiency. However, the photocatalytic degradation of the ternary nanocomposite showed performance that was two times greater than ZnO-g-C3N4, exhibiting 99.5% degradation efficiency after just 15 min of light irradiation. The combined heterojunction and synergistic effects of this composite account for the improved photocatalytic activity.