We report a novel phenazine-embedded fluorescent probe (2-[2-(pyridin-2-ylmethoxy)-phenyl]-1H-imidazo[4,5-b]phenazine, PIP), which upon complexation with Cu(II)-ion-forming [(PIP)Cu ^II (Cl)] becomes nonfluorescent but regenerates fluorescence in a selective reaction with NO and HNO over different biologically reactive oxygen and nitrogen (ROS/RNS) species under physiological conditions. The fluorescence intensity of PIP gets quenched due to the formation of the [(PIP)Cu ^II (Cl)] complex, which regenerates the fluorescence by 67 and 84% upon reaction either with NO or HNO, respectively, in the presence of other biological reducing species. Details of photophysical properties of PIP, [(PIP)Cu ^II (Cl)], and [(PIP)Cu ^I ] have been studied by density functional theory (DFT) calculations. The recognition efficacy of [(PIP)Cu ^II (Cl)] for exogenous and endogenous NO and HNO in A549 and RAW 264.7 cells with the flow cytometry application has also been demonstrated successfully.