This study investigates the use of *Mangifera indica* leaf waste-derived activated carbon as an electrode material for high-performance supercapacitors. The dried leaves were carbonized using FeCl3 and then activated with KOH at different temperatures to enhance their surface area and pore structure. The activated carbon prepared at 725 °C exhibited a high specific capacitance of 521.65 F g−1 at a current density of 0.5 A g−1 and an energy density of 17.04 W h kg−1 at a power density of 242.50 W kg−1 in a 6 M KOH electrolyte. It demonstrated remarkable electrochemical cycling stability, retaining 96.60% of its initial capacity after 10,001 cycles. The superior performance is attributed to its high surface area, well-distributed pore size, and excellent graphitization, which facilitate ion diffusion and enhance electrolyte accessibility. This research provides a promising route for utilizing waste biomass as a low-cost, sustainable electrode material for energy storage devices.This study investigates the use of *Mangifera indica* leaf waste-derived activated carbon as an electrode material for high-performance supercapacitors. The dried leaves were carbonized using FeCl3 and then activated with KOH at different temperatures to enhance their surface area and pore structure. The activated carbon prepared at 725 °C exhibited a high specific capacitance of 521.65 F g−1 at a current density of 0.5 A g−1 and an energy density of 17.04 W h kg−1 at a power density of 242.50 W kg−1 in a 6 M KOH electrolyte. It demonstrated remarkable electrochemical cycling stability, retaining 96.60% of its initial capacity after 10,001 cycles. The superior performance is attributed to its high surface area, well-distributed pore size, and excellent graphitization, which facilitate ion diffusion and enhance electrolyte accessibility. This research provides a promising route for utilizing waste biomass as a low-cost, sustainable electrode material for energy storage devices.