A redox-mediated organic electrolyte is prepared by adding P-phenylenediamine into lithium perchlorate/acetonitrile electrolyte for the application in activated carbon-based supercapacitor. The supercapacitor exhibits good cyclical stability, high specific capacitance of 68.59 F g−1, high energy density of 54.46 Wh kg−1 and high power density of 13.11 kW kg−1, which are higher than that of supercapacitor with a conventional organic electrolyte. The excellent performance of the supercapacitor is attributed to the quick reversible faradic reactions of the redox mediator (P-phenylenediamine), which accelerates the electronic migration, enhances the contact between the electrolyte and electrodes, and brings additional pseudocapacitive contribution for the system.