Hexavalent chromium is one of the most chronic and harmful to human beings, animals, and environmental well-being, and hence needs a high attention to detoxify it. For this purpose, bimetallic (In,Ga)2(O,S)3 oxy-sulfide nanoflower catalyst with different Ga contents was successfully synthesized at a low temperature of 150 °C via a facile method. It was systematically characterized and the visible light-driven photocatalytic reduction of toxic Cr(VI) was 100% completed at 4 min. The Cr(VI) reduction reaction rate constant was 13.8 fold higher than that of Ga-free In2(O,S)3 catalyst. It also showed lower recombination of photogenerated charge carriers, faster interfacial reaction rate, and higher electrical conductivity. The photoexcited electrons and H+ ions played crucial roles in the reduction of Cr(VI). The Cr(III) composition was 12.0% of the total atomic composition. The as-synthesized catalyst showed a tremendously fast Cr(VI) reduction activity and hence, it is promising for detoxification of hazardous Cr(VI).