The rapid surface oxidation of phosphorene under ambient conditions is considered to be a serious issue for many applications, but is used here as a strategy to achieve efficient heteroatom doping. Highly crystalline nitrogen-doped phosphorene (N-phosphorene) is prepared using a combination of ball milling and microwave techniques. The prepared N-doped phosphorene nanosheets showed outstanding electrocatalytic performance as a new type of non-metallic catalyst for nitrogen (N2) to ammonia (NH3) conversion, with an NH3 yield rate and faradaic efficiency (FE) of up to 18.79 μg h−1 mgCAT−1 and 21.51%, respectively, at a low overpotential (0 V) versus the reversible hydrogen electrode (RHE). Density functional theory calculations revealed that the high nitrogen reduction reaction (NRR) FEs originate from the increased hydrophobicity at the N and O doped phosphorene surfaces, which in turn hinders the competing hydrogen evolution reaction (HER) in an alkaline environment and promotes the NRR. This work not only introduces an efficient strategy to chemically functionalize 2D phosphorene, but also opens a new avenue in using N-doped phosphorene nanosheets as a metal-free catalyst.