Hydrogenation of CO2 into CH4 is an effective strategy for dealing with CO2-relevant environmental problems. Since the CO2 methanation reaction involves multiple electron transfers and various C1 intermediates, improving the reaction rate at each step is critical to accelerating the entire reaction. Here, we report a dual-active-site tandem catalyst (Ru1Ni/CeO2) composed of Ru single atoms (Ru1) and Ni nanoparticles, which can effectively convert CO2 to CH4, showing ∼90% CO2 conversion and ∼99% CH4 selectivity at 325 °C, much higher than those of the Ru1/CeO2 and Ni/CeO2 catalysts. Experimental and theoretical calculation results reveal that Ru1 is extremely active for converting CO2 to CO, while the Ni site is highly efficient for the subsequent sequential CO to CH4 reaction step. The coexistence of the Ru1 and Ni sites significantly boosts the overall reaction. This work offers a promising strategy for the rational design of efficient multisite tandem catalysts.