This study presents a novel heterogeneous Ru–S catalyst that enables chemoselective hydrogenation of sulfur-containing quinolines under mild conditions. The catalyst tolerates multiple sulfur functionalities, including thioethers, thiophenes, sulfoxides, sulfones, sulfonamides, and sulfoximines, allowing for the efficient synthesis of 1,2,3,4-tetrahydroquinolines (THQs). The catalyst's sulfur tolerance is attributed to the presence of oxidized sulfur species, which enhance catalytic activity by coordinating to the catalyst surface. The study demonstrates that the Ru–W–S–0.33 catalyst exhibits high reactivity and sulfur resistance, achieving up to 96% yield in the hydrogenation of 2-methyl-8-(methylthio)-quinoline. The catalyst also shows excellent recyclability, maintaining high activity after multiple cycles. The method is applicable to a wide range of sulfur-containing quinolines, including those with sterically demanding substituents, and can tolerate various sulfur functionalities such as dithianes, sulfoxides, sulfones, and sulfoximines. The study highlights the importance of sulfur tolerance in catalysis and demonstrates the utility of the catalyst in the synthesis of complex THQs with diverse functional groups. The results show that the catalyst can selectively hydrogenate the quinoline core while preserving other unsaturated moieties, making it a valuable tool for the synthesis of bioactive compounds. The study also demonstrates the potential of the catalyst in downstream product modifications, such as the Corey–Seebach-type umpolung of dithianes and SuFEx click reactions. Overall, this work provides a promising approach for the efficient and selective hydrogenation of sulfur-containing quinolines under mild conditions.This study presents a novel heterogeneous Ru–S catalyst that enables chemoselective hydrogenation of sulfur-containing quinolines under mild conditions. The catalyst tolerates multiple sulfur functionalities, including thioethers, thiophenes, sulfoxides, sulfones, sulfonamides, and sulfoximines, allowing for the efficient synthesis of 1,2,3,4-tetrahydroquinolines (THQs). The catalyst's sulfur tolerance is attributed to the presence of oxidized sulfur species, which enhance catalytic activity by coordinating to the catalyst surface. The study demonstrates that the Ru–W–S–0.33 catalyst exhibits high reactivity and sulfur resistance, achieving up to 96% yield in the hydrogenation of 2-methyl-8-(methylthio)-quinoline. The catalyst also shows excellent recyclability, maintaining high activity after multiple cycles. The method is applicable to a wide range of sulfur-containing quinolines, including those with sterically demanding substituents, and can tolerate various sulfur functionalities such as dithianes, sulfoxides, sulfones, and sulfoximines. The study highlights the importance of sulfur tolerance in catalysis and demonstrates the utility of the catalyst in the synthesis of complex THQs with diverse functional groups. The results show that the catalyst can selectively hydrogenate the quinoline core while preserving other unsaturated moieties, making it a valuable tool for the synthesis of bioactive compounds. The study also demonstrates the potential of the catalyst in downstream product modifications, such as the Corey–Seebach-type umpolung of dithianes and SuFEx click reactions. Overall, this work provides a promising approach for the efficient and selective hydrogenation of sulfur-containing quinolines under mild conditions.