The electrochemical behaviour of chlorpromazine (CPZ) at different pH values was studied using a fluorine-doped tin oxide (FTO) electrode. Cyclic voltammetry (CV), square-wave voltammetry (SWV), electrochemical impedance spectroscopy (EIS), and constant-potential electrolysis were used to elucidate the electrooxidation mechanism of CPZ on the FTO electrode, whereas chronoamperometry was used to determine CPZ in pharmaceutical and water samples. In addition, using mass spectrometry (MS), it was determined that the main oxidation product was the metabolite chlorpromazine sulfoxide (CPZ-SO). When electrolysis was performed at 1.45 V and pH 2, two metabolites were detected by MS, and a competitive mechanism was proposed wherein CPZ-SO was obtained simultaneously. Linear analytical curves were obtained between 2 × 10⁻⁶ and 100 × 10⁻⁶ mol L⁻¹, and the detection limit was determined to be 0.26 × 10⁻⁶ mol L⁻¹. The developed electroanalytical method thereby presents an appropriate sensitivity and stability that renders it suitable for use in the quality control and routine quantification of pharmaceutical formulations and samples containing environmentally relevant concentrations.