Thiophenol (PhSH) and hydrazine (N₂H₄) are widely present in industrial, agricultural, and food-related processes, posing significant risks to human health and environmental safety. In this study, we introduce INS (2-(benzo[ d ]thiazol-2-yl)-4-((1,3-dioxo-1,3-dihydro-2H-inden-2-ylidene)methyl)phenyl 2,4-dinitrobenzenesulfonate), a dual-responsive fluorescent probe capable of selectively distinguishing PhSH and N₂H₄ through reaction-triggered modulation of d -PET, ICT, and ESIPT processes. INS displays rapid responses (≤2 min for PhSH and ≤ 5 min for N₂H₄), high sensitivity with detection limits of 0.731 and 1.016 μM, respectively, and excellent selectivity. Mechanistic investigations using NMR, TOF-MS, and DFT analyses confirmed the distinct sensing pathways. The probe demonstrated strong applicability in real matrices, enabling quantitative detection of both analytes in soil and water with recoveries of 98.9–112.2%. Portable paper strip, cotton swab, and smartphone-assisted imaging further supported its suitability for on-site testing. Additionally, food sample analyse and live-cell imaging confirmed the biocompatibility and practical utility of INS for monitoring hazardous contaminants.