Ag–SnO₂ nanocomposites (1 mM and 3 mM) were synthesized in water at room temperature using an electrochemically active biofilm. The resulting nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, diffuse reflectance spectroscopy, photoluminescence spectroscopy and X-ray photoelectron spectroscopy. The Ag–SnO₂ nanocomposites exhibited enhanced photocatalytic activity under visible light irradiation for the degradation of methyl orange, methylene blue, 4-nitrophenol and 2-chlorophenol compared with pure SnO₂ nanostructures. Photoelectrochemical measurements, such as electrochemical impedance spectroscopy, linear scan voltammetry and differential pulse voltammetry in the dark and under visible light irradiation, further supported the visible light activity of the Ag–SnO₂ nanocomposites. These results showed that the Ag nanoparticles induced visible light activity and facilitated efficient charge separation in the Ag–SnO₂ nanocomposites, thereby improving the photocatalytic and photoelectrochemical performance.