Catalytic conversion of carbon dioxide (CO₂) into value-added chemicals is an important and active field in both of the condensed-phase and gas-phase studies. This mini-review summarizes a variety of experimentally identified reactions in the activation and transformation of CO₂ by metal species in the gas phase. The use of advanced mass spectrometric instrumentation in conjunction with quantum chemistry calculations can uncover the mechanistic details and determine the vital factors that control the activation of CO₂. This review focuses mainly on three topics: the activation of CO₂ by (1) bare metal ions and metal oxide species, (2) metal hydrides, and (3) other gas-phase metal species. Emphasis is placed on the latest advances in the hydrogenation of CO₂ mediated with metal hydrides. A potential prospect toward the future effort in the activation and transformation of CO₂ in gas phase has also been discussed.