A new ionic liquid gel polymer electrolyte based on hydrophobic ionic liquid 1-ethyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate (EMImFAP) entrapped in poly (vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) copolymer has been prepared for its application as an electrolyte in supercapacitor fabrication. The gel electrolyte film shows excellent thermal stability and remains stable in the same gel phase over a substantially wide temperature range from 5 to 90°C. The gel material possesses wider electrochemical window of ∼4.4V (−2.2 to 2.2V) and high ionic conductivity of ∼2×10−3 Scm−1 at room temperature. The solid-state supercapacitors have been fabricated with pristine and nitric acid treated MWCNT electrodes using the new ionic liquid gel polymer electrolyte. The performance characteristics of the capacitors have been evaluated by impedance spectroscopy, cyclic voltammetry, and galvanostatic charge–discharge measurements. A substantial improvement in the specific capacitance has been found due to the acid treatment of the MWCNTs. The modified MWCNT electrodes show the maximum capacitance value of ∼76Fg−1, which corresponded to the specific energy of ∼17.2Whkg−1 and specific power of ∼18.9kWkg−1 of MWCNT with ionic liquid gel polymer electrolyte based supercapacitor cells. The supercapacitor shows good cycling performance with ∼82% capacitance retention after 10,000 charge–discharge cycles.