Enhancing the separation and transfer of photogenerated carries is vital for improving the efficiency of photocatalytic hydrogen evolution reaction (HER) of graphitic carbon nitride (g-C₃N₄). Herein, a carbon-rich g-C₃N₄ with nitrogen vacancies (CCN4) was constructed by incorporating the biochar into g-C₃N₄ during a thermal polymerization in N₂ atmosphere. The doped carbon atoms replaced the bridged nitrogen and increased the delocalization π states. The synergy of the enhanced π states and nitrogen vacancy favored narrowing the bandgap and accelerating the charge separation and migration in catalyst. Meanwhile, the CCN4 catalyst had favorable kinetics for HER, with simpler steps and a lower energy barrier than the PCN sample, in which H₂ production from *H is prior to OH generation. The CCN4 catalyst exhibited excellent HER activity with a hydrogen evolution rate of 3342.4 μmol∙g⁻¹∙h⁻¹ with 0.5 wt% cocatalyst Pt, which was 5.1 times higher than that of pristine g-C₃N₄ (PCN). Additionally, CCN4 exhibited good resistance to salt with the concentration near that of natural seawater, showing the further improved hydrogen evolution rate of 3808.8 μmol∙g⁻¹∙h⁻¹. The findings reported in this work shed light on a biochar-tailored protocol to control the defects of g-C₃N₄ and optimize its intrinsic electronic properties and photocatalytic HER.