Graphitic carbon nitride (g‐C3N4) has recently been studied as a promising metal‐free catalyst for photocatalytic hydrogen generation and environmental pollution removal. However, its photocatalytic activities are far from satisfactory, partially due to unsatisfied optical absorption and poor charge separation. Hydrogenation has recently been proven as an efficient approach in enhancing the optical absorption and improving the charge separation in oxide photocatalysts. In this study, the effects of hydrogenation on nonoxide g‐C3N4 nanosheets have been elucidated for photocatalytic applications. Hydrogenation introduces structural defects, leads to disaggregation and fragmentation, and increases the specific surface area. And it increases and redshifts the optical absorption, narrows the bandgap, and increases the donor density. The photocatalytic activities are remarkably enhanced for hydrogen production from water by 45% and pollutant removal by 650% under stimulated sunlight irradiation. The enhanced photocatalytic activity is due to the synergistic effects brought by hydrogenation: the increased optical absorption, reduced bandgap, enlarged specific surface area, and increased donor density. Thus, this study shows that hydrogenation can have a wide range of effects on the structural, optical, electronic, and photocatalytic properties of g‐C3N4, providing a facile approach to modify properties and performances of nonoxide photocatalysts.