The conversion of CO2 to methane through hydrogenation with green hydrogen, known as the Power-to-Gas (P2G) process, is a promising approach to control CO2 emissions that is expected to contribute to the urgent need to mitigate global warming and climate change. Herein, the thermocatalytic CO2 hydrogenation is comparatively investigated over Ir nanoparticles dispersed on CeO2 and gadolinia-doped ceria (GDC: Ce0.9Gd0.1O2) supports, having different nano-morphologies, namely nanorods (NRs) and irregularly faceted particles (IRR). The shape of the support strongly affected the CO2 hydrogenation activity and CH4-selectivity of Ir nanoparticles, with those dispersed on nanorod-shaped CeO2,NRs and GDCNRs supports showing incredibly better performance. The best Ir/GDCNRs nanocomposite catalyst offered over 26-fold and 10-fold higher turnover frequency (TOF) at 380 °C compared to the least actives Ir/Al2O3 and Ir/CeO2,IRR, respectively −the insufficient for CO2 methanation iridium is turned into an excellent and fully selective catalyst. Combination of extensive materials characterization and kinetic results deciphered the key factors of this achievement, while the use of nanostructured supports proves to be a highly effective promotion method in heterogeneous catalysis. This work demonstrates for the first time that CeO₂ and GDC supports shaped to nanorods can turn the inefficient iridium to a highly active and selective catalyst for CO₂ methanation, well compared in activity and superior in selectivity than similarly shaped Ni/CeO2 composite catalysts.