Electrochemical nitrate reduction reaction (NtrRR) has been emerging as an appealing route for both water treatment and NH3 synthesis. Herein, we report the structure analysis and electrocatalytic performance of a novel homoleptic alkynyl-protected Ag20Cu12 nanocluster (Ag20Cu12 in short) with atomic precision, which has eight free electrons and displays characteristic absorbance feature. Single crystal X-ray diffraction (SC-XRD) discloses that, it adopts a Ag14 kernel capped by three Ag2Cu4(C≡CArF)8 metal–ligand binding motifs in the outer shell. Ag20Cu12 exhibited excellent catalytic performance toward NtrRR, as manifested by the superior NH3 Faradaic efficiency (FE, 84.6%) and yield rate (0.138 mmol·h−1·mg−1) than the homoleptic alkynyl-protected Ag32 nanoclusters. Additionally, it demonstrates good catalytic recycling capability. Density functional theory (DFT) calculations revealed that, the de-ligated Ag20Cu12 cluster can expose the available AgCu bimetallic sites as the efficient active sites for NH3 formation. In particular, the participation of Cu sites greatly facilitates the initial capture of NO3− and simultaneously promotes the selectivity of the final product. This study discovers a novel homoleptic alkynyl-protected AgCu superatom, and offers a great example to elucidate the structure–performance relationship of bimetallic catalyst for NtrRR and other multiple protons/electrons coupled electrocatalytic reactions.