In this article, square wave voltammetry was used to investigate both anodic and cathodic reactions in manganese electrowinning systems. The generated trivalent manganese ions on the anode would enter the solution and undergo a hydrolysis-disproportionation reaction in neutral or weakly acidic solutions. Nevertheless, permanganate ions would form on the electrode surface under strongly acidic conditions, which would subsequently form manganese dioxide through comproportionation reaction. At the cathode, selenium reduction is a crucial process for the deposition of manganese metal and concentration of hydrogen ions exerts a vital influence on this process by affecting the acid–base balance. Analytical methods derived from this study could also be useful for other electrometallurgical processes.