The synergistic catalysis of heterojunction electrocatalysts for the multi-step process in hydrogen evolution reaction (HER) is a promising approach to enhance the kinetics of alkaline HER. Herein, we proposed a strategy to form nanoscale Ni/NiO heterojunction porous graphitic carbon composites (Ni/NiO-PGC) by reduction-pyrolysis of the preformed Ni-metal-organic framework (MOF) under H₂/N₂ atmosphere. Benefiting from low electron transfer resistance, increased number of active sites, and unique hierarchical micro-mesoporous structure, the optimized Ni/NiO-PGC_10-1-400 exhibited excellent electrocatalytic performance and robust stability for alkaline HER (η₁₀ = 30 mV, 65 h). Density functional theory (DFT) studies revealed that the redistribution of electrons at the Ni/NiO interface enables the NiO phase to easily initiate the dissociation of alkaline H₂O, and shifts down the d-band center of Ni and optimizes the H* adsorption–desorption process of Ni, thereby leading to extremely high HER activity. This work contributes to a further understanding of the synergistic promotion of the multi-step HER processes by heterojunction electrocatalysts.