The photo-degradation of organic pollutants using solar light is an attractive chemical process for water pollution control. In this study, we synthesized a new composite material consisting of silver phosphate (Ag₃PO₄) sub-microcrystals grown on a layered molybdenum disulfide (MoS₂) and graphene (GR) hybrid as a high-performance photocatalyst for the degradation of toxic organic pollutants. This composite photocatalyst was prepared via a simple two-step hydrothermal process that used sodium molybdate, thiourea and graphene oxide as precursors for the MoS₂/GR hybrid and silver nitrate for the Ag₃PO₄ sub-microcrystals. The composite Ag₃PO₄-0.02(MoS₂/0.005GR) was found to be the most effective catalyst for the photo-decomposition of 2,4-dichlorophenol under simulated solar light and visible light (λ ≥ 420 nm). The photocatalyst was also highly active for the degradation of nitrophenol and chlorophenol. The ultra photocatalytic activity of the novel catalyst arose from the synergetic effects of MoS₂ and GR as cocatalysts in the composite. MoS₂/GR nanosheets served as electron collectors for the interfacial electron transfer from Ag₃PO₄ to electron acceptors in the aqueous solution and thus enhanced the separation of the photo-generated electron–hole pairs and made the holes more available for organic oxidation. In addition, the presence of MoS₂ and GR provided more active adsorption sites and allowed for the activation of dissolved O₂ for organic degradation in water.