Recently, Ag₃PO₄ has been demonstrated to be a new kind of material with high visible-light photocatalytic performance for the decomposition of various organic species. To further improve the photocatalytic activity of Ag₃PO₄, hole cocatalyst modification is a promising approach via the rapid transfer of photogenerated holes for effective oxidation reaction. In this work, Co-Pi as a hole cocatalyst was successfully modified on the Ag₃PO₄ surface by an in situ photodeposition method (referred to as CoPi/Ag₃PO₄). The results showed that the photocatalytic activity of CoPi/Ag₃PO₄ was greatly improved compared with that of Ag₃PO₄. Especially, CoPi/Ag₃PO₄ (0.3 wt%) reached the highest photocatalytic rate constant (k = 9.2 × 10⁻² min⁻¹), a value larger than that of Ag₃PO₄ (k = 1.4 × 10⁻² min⁻¹) by a factor of 6.6. However, it was further found that more accumulated electrons resulted in an obvious deactivation of Ag₃PO₄ due to the rapid transfer of holes by the Co-Pi cocatalyst, resulting in an obviously decreased photocatalytic performance during repeated tests. To enhance the performance stability of CoPi/Ag₃PO₄, the Cu(II) electron-cocatalyst was further loaded onto its surface to prepare the CoPi–Cu(II)/Ag₃PO₄ photocatalyst. The resultant CoPi–Cu(II)/Ag₃PO₄ not only indicated a much higher photocatalytic activity than CoPi/Ag₃PO₄, but also maintained the excellent stability, which was ascribed to the synergistic effect of Co-Pi as a hole cocatalyst and Cu(II) as an electron cocatalyst. This work may provide new insight for the development of highly stable and efficient photocatalysts for the degradation of organic pollutants.