Au-Sn/ZnO nanocatalyst was synthesized by a two-step synthetic approach in which Au-Sn alloy bimetallic nanoparticles (NPs) were incorporated into presynthesized ZnO in 1-butyl 3-methylimidazolium (BMIMBF4) ionic liquid (IL) via combustion route. The structure, morphology, and optical properties of the above synthesized material were analysed by using various analytical techniques, including X-Ray Diffraction (XRD), High Resolution Transmission Electron Microscopy (HRTEM), Energy Dispersive Spectroscopy Mapping (EDS), UV-vis Spectroscopy, Photoluminescence, Nitrogen Adsorption-Desorption, photoelectrochemical measurements and X-Ray Photoelectron Spectroscopy (XPS). The average particle size and the homogeneous distribution of Au-Sn nanoparticle over the surface of ZnO was analyzed by using TEM. XPS analysis provides information regarding the elemental structure of individual species as well as the possible electronic interaction between the nanoparticles. The photocatalytic activity of the nanocatalyst was studied towards the degradation of organic contaminants such as rhodamine B dye, 2-chlorophenol, phenol, 2,4- dichlorophenol and 2,4-dinitrophenol. After 90 min the complete degradation of Rhodamine B (95%) and phenol (94%) and its derivatives was achieved under visible irradiation. The high photoactivity of 3Au-1Sn/ZnO can be attributed to the combined effect of enhanced light absorption intensity, longer lifetime of electron-hole pair, lower electron-hole recombination rate, increased stability, higher surface area and the synergistic effect between the metal nanoparticles and support material. It is expected that our current work could open promising prospects for the utilization of Sn-based bimetallic system as a potential visible light photocatalyst for environmental applications.