Display omitted •The MoP/CN samples exhibit superior activity in CO2 reduction and H2 evolution.•The CO2 adsorption and conversion progress is well revealed in the photoreaction.•The efficient co-catalyst MoP facilitates the separation and transfer of charges. Photoreduction CO2 to hydrocarbons and photosplitting water for H2 production are the most promising, sustainable approaches for environmental pollution alleviation and solar-to-chemical energy conversion. However, developing low-cost, high efficient and stable photocatalysts remains a great challenge. Herein, we reported a novel visible-light activated MoP co-catalyst loaded g-C3N4 photocatalyst for CO2 reduction and water splitting under simulated irradiation firstly. Experimental results demonstrated that the composites were highly active and exhibited superior stability. The maximum CO and H2 evolution rates of 0.92 μmol h−1 and 40.38 μmol h−1 were achieved on MoP/CN-15% catalyst, which were 4.5-fold and 74.5-fold higher than the pure g-C3N4, and the corresponding apparent quantum efficiencies (AQE) were 3.5% and 18.3% at 420 nm, respectively. In situ FTIR analysis disclosed the CO2 adsorption and conversion progress, in which the COO− acted as a major intermediate. Furthermore, comprehensive characterization analysis revealed the introduction of MoP facilitated the separation and transfer of photogenerated electron-hole pairs, and the theoretical calculation by density functional theory (DFT) also confirmed that MoP could effectively separate the photoexcited charges from g-C3N4. Combining with experimental and DFT calculations results, a new way to design cost-effective photocatalysts has been enlightened.