The electroreduction of CO₂ to produce acetate is an extremely important and widely studied reaction. Herein, we report a heterogeneous electrocatalyst with Co₃O₄ nanoparticles immobilized on polyaniline (PANI) and cosupported by highly graphitized carbon (Co₃O₄/PANI/C) for the electroreduction of CO₂ to acetate with high activity and selectivity. Remarkably enhanced acetate Faraday efficiency (ca. 62%) and current density (ca. 35 mA∙cm⁻²) were obtained under conditions of static electroreduction at −0.95 V in 0.5 M KOH aqueous electrolyte while suppressing the competitive hydrogen evolution reaction. The excellent performance of Co₃O₄/PANI/C is attributed to the tandem effect of the Co₃O₄ nanoparticles with abundant oxygen vacancies and the PANI heterogeneous interface in a favorable configuration. Density functional theory calculations revealed that the tandem configuration of Co₃O₄/PANI/C facilitates the rapid delivery of the key *CO intermediate formed on Co₃O₄ to PANI, which increases the coverage of the intermediate *CO on the electrocatalyst surface, thus promoting acetate production during the CO₂ electroreduction reaction.