We elucidated the cooperative active sites of Ni-Pt alloy nanoparticles composed of Pt atoms isolated by Ni atoms and their neighboring Ni atoms for the efficient and selective hydrogenation of CO2 toward CH4. The stepwise methanation dynamics were revealed by in situ observations and transient changes in the infrared spectra during the hydrogenation of CO2. It was found that the hydrogenation of CO species attached to the isolated Pt atoms proceeded through a bridging CO species between isolated Pt atoms and their neighboring Ni atoms, leading to an excellent selectivity toward CH4. Kinetic studies revealed that the high H-2 dissociation ability of the Pt species accelerated the hydrogenation of the carbon species over the surface of the NiPt alloy, thereby avoiding the rate limitations of CH4 formation which are common for Ni catalysts. The bifunctional role of the isolated Pt atoms therefore allowed the efficient formation of CH4 while maintaining the excellent selectivity of the Ni catalyst toward CH4, despite Pt catalysts tending to favor CO production.