With a broader objective to replace visible light driven Pt-based photoelectrochemical/catalytic hydrogen evolution, a series of cost-effective bimetallic nanoalloys of Cu-Ag have been deposited on core-shell nanostructured SiO2@TiO2 through a facile reduction route. The physicochemical properties, i.e. crystal structure, morphology, chemical environment, and optical properties of Cu-Ag bimetal alloy decorated SiO2@TiO2 hybrid photocatalyst, have been thoroughly investigated through X-ray diffraction, high resolution transmission electron microscopy, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectroscopy, and photoluminescence spectroscopy, respectively. TEM study confirms the coating of an ultrathin layer of TiO2 shell on 100 nm sized SiO2 core, and about 4.5 nm of Ag-Cu nanoalloys are uniformly distributed on the core-shell nanostructure. The higher light absorption throughout the visible range and better separation of charge carrier by Ag-Cu (1:3) deposited SiO2@TiO2 hybrid compared to other counterparts is confirmed from UV-vis, diffuse reflectance spectroscopy, photoluminescence, and electrochemical impedance studies. Eightfold higher photocurrent enhancements, threefold enhanced photocatalytic hydrogen generation, and twofold higher phenol oxidation activities of Ag-Cu (1:3) deposited SiO2@TiO2 hybrid compared to those of the monometallic plasmonic catalyst may be attributed to the synergetic effect of enriched light harvesting and surface plasmon induced hot electron transfer from the nanoalloy to the TiO2 interface, resulting in efficient charge transfer.