Layered metal phosphorus trichalcogenides (MPX₃, M = transition metal, X = S or Se) have been established as new efficient catalysts for water splitting, with FePS₃ as one representative example. Here, a novel amine-assisted exfoliation strategy is presented to obtain few-layer FePS₃ nanosheets, whose intrinsic electrical conductivity can be easily regulated by adjusting the reaction temperature. The improved electrical conductivity originates from the increase of the Fe³⁺/Fe²⁺ ratio, while matrix crystallinity also plays a vital role in this aspect. The combined effect of mixed valence and crystallinity results in superior HER performance with a decrease of the overpotential of 147 mV and a drop of the Tafel slope from 139 mV dec⁻¹ to 94 mV dec⁻¹.