A simple phenoxazine-based fluorescence chemosensor N-(4-((4-((5-oxo-5H-benzo [a]phenoxazin-6-yl)amino)phenyl)sulfonyl)phenyl)furan-2-carboxamide (NPC) was developed for discriminative detection of Cd2+ and CN− ions. This easily available chemosensor was synthesized by adding a furan-2-carboxamide group to a phenoxazine fluorophore and a phenyl sulfonyl chelating site. The sensor NPC exhibited turn-on fluorescence emission for Cd2+, and the obtained NPC–Cd2+ complex detected CN− via turn-off fluorescence response with 2:1 binding stoichiometry in CH3CN/H2O (99:1 v/v) medium by fluorescence spectroscopy. The detection limits of Cd2+ and CN− were 0.60 μM and 0.145 μM, respectively, which were significantly lower than the World Health Organization guidelines. The proposed mechanism of sensor NPC was additionally supported by NMR, FT-IR analyses, DFT and a UV/visible titration studies. Furthermore, the sensor NPC has been successfully demonstrated as a biomarker for detecting Cd2+ in live cells and zebrafish larvae.