The prime objective of the present article is to develop an efficient supercapacitor based on polymer electrolyte doped with salt. Solution cast technique was adopted to develop a solid polymer electrolyte of polymer poly(methyl methacrylate) (PMMA) as host polymer and salt potassium hydroxide (KOH) as a dopant. Incorporation of salt increases the amorphicity and assisted in conductivity enhancement. Moreover, doping of salt increases the overall conductivity of polymer electrolyte film. Electrochemical impedance spectroscopy reveals the enhancement in conductivity (four orders of magnitude) by salt doping. Fourier transform infrared shows the complexation and composite nature of films. Polarized optical microscopy shows the reduction in crystallinity, which is further confirmed by Differential scanning calorimetry. Fabricated electrochemical double-layer supercapacitor using maximum conducting polymer-salt electrolyte and symmetric carbon nanotubes electrodes shows specific capacitance of 21.86 F g(-1).