The electrocatalytic nitrogen reduction reaction (NRR) offers a sustainable route for ammonia synthesis but is severely hindered by the inertness of N2, its low solubility, and the competing hydrogen evolution reaction (HER). To address this trilemma, a scalable one pot pyrolysis method was employed to fabricate a heterostructure catalyst comprising Fe3C/Fe nanoparticles embedded within a nitrogen-doped carbon matrix (Fe3C/Fe@NC). In KOH electrolyte, this catalyst achieves a high NH3 yield of 8.0 µg h−1 mgcat−1 and a faradaic efficiency of 8.7%, and good long-term stability. The performance enhancement arises from a synergistic design. The nitrogen-doped carbon ensures high conductivity and mass transport, while the strong interfacial electronic coupling within the Fe3C/Fe heterostructure simultaneously strengthens N2 chemisorption and activation, lowers the energy barrier for the rate-determining step (RDS), and optimizes hydrogen adsorption to effectively suppress the HER. This work provides a robust and rational heterostructure engineering strategy for advancing ambient NRR electrocatalysis.