Developing low-cost and high-efficiency photocatalysts for hydrogen production from solar water splitting is an intriguing and challenging objective. Co–P-based ternary alloy Co–M–P (M: Cu, Ni) cocatalysts decorated on graphene (GP) were prepared by doping Cu and Ni via an in situ synthesis strategy, and the photocatalytic performances for H₂ generation were systematically studied under visible light irradiation. The structure, morphology, chemical composition, and surface electronic state of the catalysts were studied using X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) techniques. The results indicated that the Co–Cu–P and Co–Ni–P alloys were active co-catalysts for photocatalytic H₂ evolution under visible light irradiation, and the partially oxidized Co species played an important role in enhancing efficient H₂ generation evidenced by XPS and XRD characterizations. For the Co–Cu–P/GP (15%) and Co–Ni–P/GP (15%) catalysts, the H₂ generation rates reached 44.5 and 36.1 mmol h⁻¹ g_Co⁻¹, respectively. The apparent quantum efficiency (AQE) of Co–Cu–P/GP (15%) and Co–Ni–P/GP (10%) samples reached 23.6 and 14.8% at 430 nm, respectively. Multi-cycle experiments indicated that both Co–Cu–P/GP (15%) and Co–Ni–P/GP (10%) catalysts presented a good stability in photocatalytic H₂ evolution reactions. The Co–Ni–P and Co–Cu–P alloy materials are promising catalysts for photocatalytic H₂ evolution.