The oxidative dehydrogenation of propane with CO₂ (CO₂-ODP) is a promising technology for the efficient production of propene in tandem with CO₂ reduction to CO. However, the rational design of high-performance catalysts for this green process is still challenged by limited understanding of the nature of active sites and the reaction mechanism. In this work, the effects of SnO₂ promoter on Pt/CeO₂ activity and propene selectivity in CO₂-ODP are elucidated through varying the Sn/Pt molar ratio. When the ratio increases, propane conversion gradually decreases, while the propene selectivity increases. These dependences are explained by increasing the electron density of Pt through the promoter. The strength of this effect is determined by the Sn/Pt ratio. Owing to the electronic changes of Pt, CO₂-ODP becomes more favorable than the undesired CO₂ reforming of propane. Sn-modified Pt–O–Ce bonds are reasonably revealed as the active sites for CO₂-ODP occurring through a redox mechanism involving the activation of CO₂ over oxygen vacancies at Sn-modified Pt and CeO₂ boundaries. These atomic-scale understandings are important guidelines for purposeful development of high-performance Pt-based catalysts for CO₂-ODP.