Peroxymonosulfate (PMS)-assisted photocatalytic degradation represents an efficient advanced oxidation process for water purification. In this study, a novel SrTiO₃/Cu₂SnS₃ heterojunction was synthesized via a hydrothermal method, which was employed for visible-light-driven PMS activation to degrade norfloxacin (NOR). The STO/CTS-2 (nSrTiO₃/nCu₂SnS₃ = 2) composite exhibited superior catalytic performance, achieving 92.65% NOR degradation within 60 min, attributed to enhanced charge separation and efficient PMS activation. Comprehensive characterization confirmed the heterostructure formation, optimized band alignment, and improved light absorption. Radical trapping experiments revealed that superoxide radicals (•O₂⁻) dominated the degradation process, with additional contributions from SO4•⁻, •OH, 1O2, and h⁺. A plausible NOR degradation pathway and the underlying PMS activation mechanism were proposed. This study provides new insights into visible-light-driven PMS activation and presents an effective strategy for antibiotic wastewater treatment.