The rapid development of clean energy generation devices has invaded every nook and corner of cutting-edge technology. With time, supercapacitors play a foremost role as a promising candidate in energy storage systems. However, electrode material becomes a decisive factor in the electrochemical performance of the supercapacitor and its capacitance can be controlled by using activated agents. Herein, the electrochemical window of the highly porous nitrogen-doped activated carbon was enhanced through the process of carbonization and activation of polyaniline nanotubes with KOH. Polyaniline nanotubes were synthesized using a facile oxidative polymerization process. Moreover, the changes in surface area and porosity were examined via BET analysis for the samples having polyaniline to KOH ratio 1:0.5, 1:1, and 1:2. It was observed that the surface area and pore volume from as-synthesized polyaniline to chemically treated samples was significantly improved from 18 to 3525 m²/g. The highest specific capacitance of 317 F/g was observed at the current density of 1A/g for polyaniline activated using 1:1 ratio of an activating agent. The sample achieved a maximum energy density of 36 Wh/kg with a power density of 455 W/kg. Further, these supercapacitors provided a good coulombic efficiency of about 100% with capacitance retention of 92% after 5000 charge-discharge cycles. The research suggests our facile approach to synthesizing nitrogen-doped carbon for supercapacitors could be adopted for commercial applications.