LaNi5 alloy can be utilized to directly store and release hydrogen in mild condition, thus it is considered as a long-term safe and stable solid-state hydrogen storage material. In this work, LaNi5H5 was used as the solid-state hydrogen source in the CO2 methanation reaction. Impressively, the carbon dioxide conversion can be achieved to nearly 100% under 3 MPa mixed gas at 200 °C. The microstructure and composition analysis results reveal that the high catalytic activity may originate from the promoted elementary steps over in situ formed metallic Ni nanoparticles during the CO2 methanation process. More importantly, as the lowered reaction temperature prevented the agglomeration of Ni nanoparticles, this catalyst exhibited durable stability with 99% conversion rate of CO2 retained after 400 h cycling test.