Graphitic carbon nitride, a 2 D layered photocatalyst coupled with transition metal oxides often shows promising photocatalytic hydrogen evolution activity. However, low surface area and poor charge separation greatly hinder its photocatalytic efficiency. A Ni+x(x=2, 3)/O−g‐C3N4 photocatalyst with a very high specific surface area (199 m2 g−1) has been prepared by thermal condensation and wet‐impregnation methods. The oxygen‐functionalized and Ni+x(x=2, 3)‐coordinated g‐C3N4 produced 1664 μmol g−1 of hydrogen evolution from water under direct solar light irradiation in 4 h, which is 23 times higher than that over O−g‐C3N4. This significant enhancement results from the combined effects of large surface area, the formation of long‐life deep‐trap states, effective charge carrier separation, and extended visible light absorption. The separation and transport behavior of the charge carriers are investigated by photoluminescence, time‐resolved photoluminescence, photocurrent and Mott–Schottky measurements. Additionally, the interaction between Ni+x(x=2, 3) and O−g‐C3N4 is studied by X‐ray photoelectron spectroscopy, X‐ray diffraction, and FTIR spectroscopy. The Ni+x(x=2, 3)/O−g‐C3N4 photocatalyst shows remarkable reusability over a period of two months (six cycles). This study may provide a pathway to simultaneously overcome the challenges of low surface area and poor charge separation in g‐C3N4‐based photocatalysts.