Nanocrystalline N-doped SiO₂/TiO₂ visible-light photocatalyst thin films were synthesized using the sol-gel method on glass substrates. The synthesized catalysts were then characterized using several analytical techniques like x-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), and UV–vis absorption spectroscopy (UV–vis). The experimental results revealed that the maximum optical response of the synthesized SiO₂/TiO₂ thin films shifted from the ultraviolet (UV) to the visible-light region (λ⩾420 nm). The photocatalytic activity of N-doped SiO₂–TiO₂ photocatalyst was considerably higher than that of SiO₂–TiO₂, and this result was obtained with an optimal concentration of 40 mol% of N. The enhanced photocatalytic activity was attributed to the increasing surface area and forming more hydroxyl groups in the doped catalyst.