Under visible-light irradiation, graphitic carbon nitride (g-C₃N₄) is considered a favorable photocatalyst for hydrogen (H₂) production from water splitting. However, the poor H₂ production and fast recombination rate of charge carriers prevent its practical applications. Therefore, the integration of g-C₃H₄ with suitable plasmonic materials to develop a nanocomposite photocatalyst is worthwhile for enhancing H₂ evolution. Herein, a highly efficient g-C₃N₄/Ni@N-doped C (termed as CN/Ni@C) plasmonic photocatalyst is developed by the combination of g-C₃N₄ and nickel supported on nitrogen-doped carbon (Ni@C) for H₂ production from water splitting. The results show that photocatalytic performance is enhanced by Ni metallic plasmons over the CN/Ni@C nanocomposite. The optimized CN/Ni@C-1 (1 wt% Ni@C loading) plasmonic heterojunction achieves an efficient H₂ evolution rate of 56.67 μmol h⁻¹, which is 4-fold higher than that of bare g-C₃N₄ (13.55 μmol h⁻¹) with an apparent quantum yield (AQY) of 5.20% under visible-light irradiation (λ ≥ 420 nm). This improved performance is associated with the efficient charge separation, charge transfer, and surface plasmon resonance (SPR) effect of metallic Ni nanoparticles. Additionally, the optimal CN/Ni@C-1 plasmonic heterojunction exhibits excellent photocatalytic stability toward H₂ generation. We believe that this study will open the door to constructing and developing other plasmonic material decorated g-C₃N₄ photocatalysts for potential applications in sustainable and renewable energy.