Nanoscale zero-valent iron has been considered to be the most promising electrocatalyst for denitrification due to its abundant resources, low price and non-toxicity. Nevertheless, the low utilization of active ingredients, inferior removal capacities (mg N g⁻¹ Fe), and poor nitrogen selectivity are still major challenges during practical nitrate reduction. Herein, we have synthesized a one-dimensional architecture with homogeneously distributed Fe/Fe₃C nanoparticles immobilized in a monodispersed carbonaceous matrix, embedded in ultra-high N-doped carbon nanofibers (Fe/Fe₃C-NCNF) via a simple electrospinning strategy followed by confined reduction under a H₂ atmosphere. The as-prepared Fe/Fe₃C-NCNF nanostructure features well-dispersed Fe/Fe₃C nanoparticles, confined reactive spaces, an interconnected nanofiber framework, and rich nitrogen doping sites, which are beneficial for integrating the synergistic catalytic effect of Fe and Fe₃C, providing high-reactivity sites, boosting electron transfer, enlarging the catalyst–electrolyte interface and enhancing the surface adsorption capacity. The results reveal ultra-high nitrogen selectivity of 95% within 6 h and nearly 100% in 12 h, which are superior to other reported catalysts, and a maximum removal capacity of 2928.42 mg N g⁻¹ Fe can be achieved, greatly improving the utilization of active ingredients. In addition, the catalysis material also shows good catalysis stability due to its structural features. The results of this study provide broad potential for the further development of iron-based functional nanostructures for electrocatalytic denitrification.