For most metal-containing CO₂ reduction reaction (CO₂RR) electrocatalysts, the unavoidable self-reduction to zero-valence metal will promote hydrogen evolution, hence lowering the CO₂RR selectivity. Thus it is challenging to design a stable phase with resistance to electrochemical self-reduction as well as high CO₂RR activity. Herein, we report a scenario to develop hydrocerussite as a stable and active electrocatalyst via in situ conversion of a complex precursor, tannin-lead(II) (TA-Pb) complex. A comprehensive characterization reveals the in situ transformation of TA-Pb to cerussite (PbCO₃), and sequentially to hydrocerussite (Pb₃(CO₃)₂(OH)₂), which finally serves as a stable and active phase under CO₂RR condition. Both experiments and theoretical calculations confirm the high activity and selectivity over hydrocerussite. This work not only offers a new approach of enhancing the selectivity in CO₂RR by suppressing the self-reduction of electrode materials, but also provides a strategy for studying the reaction mechanism and active phases of electrocatalysts.