Electrochemical nitrate reduction reaction (NO₃RR) represents a prospective approach to convert the hazardous NO₃⁻ waste into valuable NH₃ product. Yet, designing highly efficient and durable catalyst with high NH₃ formation selectivity is still challenging. Herein, we report a catalyst of Ru SAs/Co-NC with Ru single atoms (Ru SAs) anchored on Co, N co-doped carbon materials (Co-NC) for efficient NO₃RR catalysis to generate NH₃. The Ru single atoms were prepared through in-situ transformation of metal nodes in metal–organic frameworks (MOFs), and the confinement in MOFs ensured the atomical dispersion of Ru atoms. The Ru SAs/Co-NC catalyst exhibited excellent catalytic performance toward NO₃RR, evidenced by a NH₃ Faradaic efficiency of 96.3% and yield rate of 1.12 mmol·h⁻¹·cm⁻² at −0.5 V vs. reversible hydrogen electrode (RHE), as well as good cycling stability. The density functional theory calculations revealed a Ru–Co synergistic catalytic effect, where the Co site promotes H₂O dissociation to supply sufficient *H for continuous hydrogenation/deoxygenation, and the Ru site is able to achieve enhanced NO₃⁻ adsorption and accelerated hydrogenation process to form NH₃ eventually.