•SnO2–CNT nanocomposites were prepared with thiolated CNTs.•SnO2–CNTs displayed high photocatalytic activities for MB and MO degradation.•The incorporated CNTs acted as electrical conductors.•A plausible photocatalytic mechanism is proposed. Tin oxide–carbon nanotube (SnO2–CNT) nanocomposites were prepared by depositing SnO2 nanoparticles onto thiolated CNT surfaces to develop highly efficient photocatalysts. The structure of SnO2–CNTs was characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the sample was benchmarked using the photodegradation of methylene blue (MB) and methyl orange (MO) in aqueous solution under UV–vis light irradiation. The SnO2–CNTs exhibited enhanced photocatalytic activities compared with bulk SnO2, SnO2 nanoparticles, and commercial P25 TiO2. The enhanced activity was ascribed to the CNT addition. The presence of CNTs effectively suppressed an electron–hole recombination and favored a reactant and product mass transport. A plausible photocatalytic mechanism is proposed.