AbstractMonitoring and controlling the reconstruction of materials under working conditions is crucial for the precise identification of active sites, elucidation of reaction mechanisms, and rational design of advanced catalysts. Herein, a Bi‐based metal–organic framework (Bi‐MOF) for electrochemical CO₂ reduction is selected as a case study. In situ Raman spectra combined with ex situ electron microscopy reveal that the intricate reconstruction of the Bi‐MOF can be controlled using two steps: 1) electrolyte‐mediated dissociation and conversion of Bi‐MOF to Bi₂O₂CO₃, and 2) potential‐mediated reduction of Bi₂O₂CO₃ to Bi. The intentionally reconstructed Bi catalyst exhibits excellent activity, selectivity, and durability for formate production, and the unsaturated surface Bi atoms formed during reconstruction become the active sites. This work emphasizes the significant impact of pre‐catalyst reconstruction under working conditions and provides insight into the design of highly active and stable electrocatalysts through the regulation of these processes.