Searching for electrocatalysts for the electrochemical CO reduction reaction (e-CORR) with high selectivity and stability remains a significant challenge. In this study, we design a Cu-CuInO composite with stable states of Cu/Cu by electrochemically depositing indium onto CuCl-decorated Cu foil. The catalyst displays superior selectivity toward the CO product, with a maximal Faraday efficiency of 89% at −0.9 V vs the reversible hydrogen electrode, and maintains impressive stability up to 27 h with a retention rate of >76% in Faraday efficiency. Our systematical characterizations reveal that the catalyst’s high performance is attributed to CuInO nanoparticles. First-principles calculations further confirm that CuInO(012) is more conducive to CO generation than Cu(111) under applied potential and presents a higher energy barrier than Cu(111) for the hydrogen evolution reaction. These theoretical predictions are consistent with our experimental observations, suggesting that CuInO nanoparticles offer a facile catalyst with a high selectivity and stability for e-CORR.