Electrocatalytic reduction of N2 to NH3 under an ambient atmosphere is highly desirable and extremely critical for energy-efficient nitrogen utilization. Inspired by the natural MoFe protein-based enzyme, the nitrogenase, we exploited this electrochemical process with a unique two-dimensional catalyst, namely, molybdenum carbide (Mo2C). The catalyst is synthesized through a chemical vapor deposition method, with a highly orientated (200) facet of the α-Mo2C phase. A remarkable Faradaic efficiency as high as 40.2% has been achieved on the (200) faceted α-Mo2C during the nitrogen reduction reaction (NRR). Density functional theory calculations confirm that rate-determining steps *NNH2 → *NNH3 and *NH → *NH2 experience a low energy barrier on the (200) surface following the proton–electron coupled, distal associated mechanism. To protect Mo from leaching during the NRR process, we also grew layers of graphene on top of Mo2C, forming a chemically enduring two-dimensional heterostructured electrode.