Photocatalytic reduction of CO₂ into high value-added CH₄ is a promising solution for energy and environmental crises. Integrating semiconductors with cocatalysts can improve the activities for photocatalytic CO₂ reduction; however, most metal cocatalysts mainly produce CO and H₂. Herein, we report a cocatalyst hydridation approach for significantly enhancing the photocatalytic reduction of CO₂ into CH₄. Hydriding Pd cocatalysts into PdH_0.43 played a dual role in performance enhancement. As revealed by our isotopic labeling experiments, the PdH_0.43 hydride cocatalysts reduced H₂ evolution, which suppressed the H₂ production and facilitated the conversion of the CO intermediate into the final product: CH₄. Meanwhile, hydridation promoted the electron trapping on the cocatalysts, improving the charge separation. This approach increased the photocatalytic selectivity in CH₄ production from 3.2% to 63.6% on Pd{100} and from 15.6% to 73.4% on Pd{111}. The results provide insights into photocatalytic mechanism studies and introduce new opportunities for designing materials towards photocatalytic CO₂ conversion.