Electrochemical N₂ fixation represents a promising strategy toward sustainable NH₃ synthesis, whereas the rational design of high-performance catalysts for the nitrogen reduction reaction (NRR) is urgently required but remains challenging. Herein, a novel hexagonal BN quantum dots (BNQDs) decorated Nb₂CT_x–MXene (BNQDs@Nb₂CT_x) is explored as an efficient NRR catalyst. BNQDs@Nb₂CT_x presents the optimum NRR activity with an NH₃ yield rate of 66.3 µg h⁻¹ mg⁻¹ (−0.4 V) and a Faradaic efficiency of 16.7% (−0.3 V), outperforming most of the state-of-the-art NRR catalysts, together with an excellent stability. Theoretical calculations revealed that the synergistic interplay of BNQDs and Nb₂CT_x enabled the creation of unique interfacial B sites serving as NRR catalytic centers capable of enhancing the N₂ activation, lowering the reaction energy barrier and impeding the H₂ evolution.