As a carbon-neutral alternative to the Haber-Bosch process, electrochemical N₂ reduction enables environment-friendly NH₃ synthesis at ambient conditions but needs active electrocatalysts for the N₂ reduction reaction. Here, we report that conductive metal-organic framework Co₃(hexahydroxytriphenylene)₂ (Co₃HHTP₂) nanoparticles act as an efficient catalyst for ambient electrochemical N₂-to-NH₃ fixation. When tested in 0.5 M LiClO₄, such Co₃HHTP₂ achieves a large NH₃ yield of 22.14 μg·h^-1·mg^-1_cat. with a faradaic efficiency of 3.34% at -0.40 V versus the reversible hydrogen electrode. This catalyst also shows high electrochemical stability and excellent selectivity toward NH₃ synthesis.