This paper investigates the enhanced pseudocapacitive properties of cobalt-doped manganese oxide (Co-doped MnO2) electrode in magnesium sulfate (MgSO4) electrolyte for supercapacitor applications. Co-doped MnO2 was synthesized on nickel foam through a controlled hydrothermal process and specific heat treatment parameters. This resulted in the transformation into α-MnO2 with a 2 × 2 tunnel structure. Morphological investigation illustrates the presence of a hierarchical micro-flower structure with a substantial surface area and mesoporous distribution. The specific surface area of the Co-doped MnO2 electrode significantly increased to 158 m2 g−1, compared to the pristine (bare MnO2) electrode (80 m2 g−1). Electrochemical analyses revealed a specific capacitance of 527 F g−1 at 1 A g−1 in MgSO4 (1 M), showcasing a 1.6 times improvement over Na2SO4 (1 M). The unique structure of the Co-doped MnO2, combined with magnesium ions as efficient electron donors, contributes to superior charge-storage, making it a promising candidate for high-performance supercapacitors. Comprehensive characterizations, such as XRD, XPS, BET, SEM, GCD, and EIS, confirm the advantageous electrochemical performance and durability of the Co-doped MnO2 electrode in MgSO4 electrolyte.