The electrocatalytic nitrogen reduction reaction (NRR) is proposed as an alternative to the Haber–Bosch process, but the development of efficient NRR electrocatalysts remains a challenging task. MoSe₂ has superior conductivity compared to MoS₂, making it promising in the NRR field. Unfortunately, the scarcity of active sites and competitive hydrogen evolution reaction (HER) hinder its broader applications. Here, Se-vacancy-rich MoSe₂ is designed through Cr doping, allowing for targeted regulations of architectural and electronic structure by leveraging the dual effects of doping and V_Se. Further mechanistic studies innovatively find that the Cr-induced multi-vacancy (18.75% concentration) exerts inverse contributions to NRR on 2H- and 1T-MoSe₂, reflecting boosted and depressed effects, respectively. Consequently, suitable doping effectively facilitates NRR and eases the competition from HER, realizing excellent NH₃ yield (51.53 ± 2.45 µg h⁻¹ mg⁻¹_cat) and Faradaic efficiency (63.37%) in MSC-1. This work paves the opportunity for MoSe₂-based electrocatalysts toward boosted NRR.