Electrocatalytic reduction of nitrogen oxides (NOx) to ammonia (NH3) offers a sustainable strategy for mitigating nitrogen pollution while providing an alternative to the energy-intensive Haber–Bosch process. However, achieving high activity and selectivity remains challenging due to sluggish multielectron transfer kinetics and competing hydrogen evolution. Herein, we develop a Co–Ru dual-atom catalyst anchored on porous nitrogen-doped carbon nanofibers (CoRu–DAC–PCF) for efficient electrochemical NO2– reduction under ambient conditions. Theoretical calculations and structural analyses show that atomically dispersed Co–Ru sites coordinated with nitrogen, enabling Co to promote water dissociation and Ru to facilitate NO2– adsorption. Spectroscopic results reveal electronic coupling and charge redistribution between adjacent Co and Ru atoms, thereby modulating the local electronic structure and optimizing the adsorption energetics of reaction intermediates and thus markedly enhancing the catalytic activities. As a result, CoRu–DAC–PCF achieves an NH3 yield rate of ∼9.8 mg h–1 cm–2 with a maximum Faradaic efficiency of ∼75% at −0.2 V vs RHE and ∼10.5 mg h–1 cm–2 at −0.7 V vs RHE with high stability over 10 cycles, highlighting the effectiveness of dual-atom site engineering for efficient ammonia electrosynthesis.