Cy3 is a dye that has been widely applied in fluorescence microscopy and single molecule detection due to its low hydrophobicity and intense fluorescence emission. As a new application, this study proposes using Cy3 as the fluorophore of a peroxyoxalate chemiluminescence system. The system relies on the oxidative reaction of bis-(2,4,6-trichlorophenyl) oxalate (TCPO) with H2O2 in the presence of imidazole, as the catalyst, to produce dioxetane via a chemically initiated electron exchange luminescence (CIEEL) process, excite Cy3 by the excess energy of the dioxetane and permit Cy3 to emit yellow light. The chemiluminescence behavior of the system is investigated using different concentrations of TCPO, imidazole, the oxidant and Cy3 and by considering non-linear least squares curve fitting of the obtained intensity–time profiles into the pooled intermediate model. The evaluated kinetic parameters include experimental and theoretical maximum intensity, the rise and fall rate constants of the chemiluminescence process, experimental and theoretical time required to reach the maximum intensity and total emission yield. Finally, the developed system is adopted to detect a drug, i.e., carvedilol, in different pharmaceuticals. Under the optimal conditions, the system can provide a linear response for determination of 3 × 10− 7 to 3 × 10− 5 M carvedilol (r > 0.9869, n = 6) and a detection limit of 1.21 × 10− 7 M. The relative standard deviation of the detection results for six repetitive determinations is below 3.47% and the obtained recoveries are 99.6% and 101.9%.