The electrochemical nitrate reduction reaction (eNO3RR) is an appealing technology for converting environmentally toxic NO3− to ammonia (NH3). This approach was usually obstructed by the multi-proton/electron involved process. Here, we report a catalyst with Ru single atoms supported on Co3O4 (Ru SAs-Co3O4). The as-developed Ru SAs-Co3O4 catalyst shows a remarkable NH3-evolving activity with a faradic efficiency of 94.92% ± 4.02% at the potential of −0.2 V (vs. RHE) and a generation rate of 1,843.45 ± 57.14 μmol h−1 cm−2 at the potential of −0.5 V. Further investigations revealed that the Ru SAs play a dual role in simultaneously accelerating the proton transfer and modulating the d-electron structures of the neighboring Co sites, which led to a lower energy barrier of the rate-determining step. Eventually, by combining the eNO3RR and electrosynthesis of 5,5′-azotetrazolate at a two-electrode system, an energy-saving NH3 synthesis, while simultaneously producing value-added chemicals, was successfully achieved.