CO₂ activation and transformation processes are essential for sustainable energy development and environmental remediation. In this review, we describe our advances in the use of gas-phase ions to mediate these processes, which have provided unique molecular-level mechanistic insights by combining mass spectrometry and density functional theory calculations. This review is structured around three fundamental CO₂ transformation reactions: reduction to CO through O-atom transfer to a suitable oxygen acceptor, B–C bond formation via reactions with metal borides, and C–N bond formation via coupling with NH₃ or N₂. The fundamental knowledge uncovered in these gas-phase studies establishes a foundational framework for future research and the rational design of novel catalytic systems for CO₂ conversion.