Electrocatalytic NO-to-NH3 conversion (NORR) provides a fascinating route toward the eco-friendly and valuable production of NH3. In this study, amorphous FeS2 (a-FeS2) is first demonstrated as a high-efficiency catalyst for the NORR, showing a maximum FENH3 of 92.5% with a corresponding NH3 yield rate of 227.1 μmol h-1 cm-2, outperforming most NORR catalysts reported earlier. Experimental measurements combined with theoretical computations clarify that the exceptional NORR activity of a-FeS2 originates from the amorphization-induced upshift of the d-band center to promote the NO activation and NO-to-NH3 hydrogenation energetics.