Metal–organic frameworks (MOFs) can electrochemically reduce nitrogen and thus can be considered as a potential electrocatalyst for converting atmospheric N₂ into useful ammonia. In this work, we fabricate a class of zero-dimensional (0D), bimetallic nickel, iron–MOFs with greatly promoted activity for the nitrogen electroreduction reaction, affording a faradaic efficiency of 11.5% and ammonia yield rate of 9.3 mg h⁻¹ mg_cat⁻¹ at −345 mV versus the reversible hydrogen electrode (RHE). Mechanistic investigations through density functional theory (DFT) calculations highlight the iron doping effect (3.1 wt% of Fe) that can suppress the energy barrier of the first ammonia release step with significantly decreased Gibbs free energy. Further, a combination of experimental studies underline the downsizing of the MOF that contributes to the optimal electronic structures of metal active sites for NN activation, in addition to enlarged porosity for facilitating reaction kinetics at electrode/electrolyte interfaces. This new emerging class of 0D, bimetallic MOF catalysts with remarkable electronic and structural features would not only constitute a very promising candidate for low-cost, efficient nitrogen fixation, but also holds great potential for many other technical applications.