Abstract: Indium-based materials have emerged as promising alternative catalysts for the selective electroreduction of CO₂ to formate, yet the optimal catalytic configuration remains elusive. Herein, theoretical calculation reveals that metallic indium over oxygen vacancy-containing In₂O₃ support (In/In₂O₃-V_O) possesses the lowest energy barriers (0.99 eV) for CO₂ reduction to formate. A rational air-annealing strategy applied to In³⁺-adsorbed resin is developed to synthesize indium oxide catalysts containing oxygen vacancy (R-In₂O₃). In-situ spectroscopy techniques confirm in-situ electrochemical reconstruction of the In/In₂O₃ configuration and the effective stabilization of the key reaction intermediate (HCOO*). Consequently, the catalyst delivers excellent CO₂-to-formate conversion performance, maintaining a current efficiency above 92% over 56 h of galvanostatic electrolysis at 250 −mA·cm⁻². These insights provide an effective strategy for the rational design of high‐performance and durable indium‐based electrocatalysts for sustainable formate production.