One conceptually different approach has been developed to synthesize Ti3+ self-doped TiO2−x mesocrystals to narrow the band gap of TiO2. This simple and economical one-pot solvothermal method uses TiCl3 and tetrabutyltitanate (TBT) as a precursor and exhibits practical application. Different morphology including uniform spindle shape, tetragonal bipyramid, and capsule-like mesocrystals can be tailored easily by tuning the precursor ratio of TiCl3 to TBT. We have shown that our band gap engineered TiO2−x exhibits unique mesocrystal phase and owns substantial high visible light driven photocatalytic activities. Electron paramagnetic resonance (EPR) studies of this sample verified the presence of oxygen centered radicals, namely, hydroxyl (·OH) and superoxide radicals (O2 −·/·OOH). The catalysts have been characterized using transmission electron microscope, fluorescence spectra, Raman spectra, EPR, X-ray photoelectron spectroscopy, X-ray diffraction (XRD), Ultraviolet–visible absorption spectra, etc. It shows high catalytic stability. The findings of this work provide new insights for developing morphology tailored for visible light driven devices and other applications via controlled band gap engineering.