Since the alkaline hydrogen evolution reaction (HER) on benchmark Pt/C is heavily limited by the sluggish water dissociation step, and pure Pt catalysts generally suffer from high cost and poor durability, constructing well-dispersed nanoalloys composed of Pt and appropriate earth-abundant transition metals strongly adhering to the carbon support provides a comprehensive strategy to address these issues simultaneously. Here, a simple pyrolysis approach was developed to fabricate uniform PtNi nanoparticles with dominant exposure of the highly active (111) surface in situ grown on the branched N-doped carbon framework. The optimized PtNi-NC-900 catalyst achieved outstanding HER performance with a mass activity of 3.78 A mg_Pt⁻¹ and a current attenuation of ∼10% within 20 h of HER operation in 1.0 M KOH, outperforming that of commercial 20 wt% Pt/C (i.e., 0.27 A mg_Pt⁻¹ and ∼30% current loss). DFT computations further reveal that the rational alloying of Pt and Ni elements is beneficial for modifying their mutual electron distributions and d-band center positions, which allow accelerating the dissociation of *H₂O with a much lower energy barrier of 0.289 eV than the 0.620 eV for the Pt(111) surface and suitable binding strengths of other alkaline HER intermediates on different active sites, thereby contributing to synergistic catalysis on alkaline HER.