Monoclinic clinobisvanite BiVO4 is one of the most promising photocatalyst due to its stability, low cost, narrow band gap, and suitable valence band maximum (VBM) position. The valence band maximum of about -7.10 eV at vacuum level was observed, which is well below the redox potential of water. However, the conduction band minimum, CBM of about - 4.86 eV at vacuum level, which was responsible for its low efficiency. The presence of metal (Si or V) vacancy changed the charge density and VBM of pristine BiVO4. Our calculated results revealed that 0.04% of the intrinsic Bi or V defects enhanced p-type conductivity and hence improved photocatalytic activity than O-interstitial in pristine BiVO4. The optical properties of both pristine and intrinsically defective BiVO4 were calculated and analyzed with perspective of their photocatalytic properties. Conclusively, the role of Bi or V (metal) vacancies in pristine BiVO 4 was found to be significant than O interstitials in enhancing the photocatalytic properties regarding the solar water splitting.