Most porous carbons have been prepared using KOH, ZnCl2 as activating agents via chemical activation process, where toxic chemicals, elevated temperature and multi-stage preparation are involved. Herein, we report synthesis of porous carbon from hemp fibre (HFPC) via single step, low temperature carbonization followed by CO2 physical activation for high-performance solid state supercapacitor application in a PVA-KOH hydrogel as gel electrolyte. Detailed characterization and optimization studies based on varying the duration (hours) of activation yields HFPC-30 material that comprises of interconnected carbon network of meso and macro pores with a high specific surface area of 1060 m2g−1. This enables rapid ion transfer and efficient electrode- electrolyte interaction and HFPC-30 exhibit an excellent half-cell specific capacitance of ~600 Fg−1 at 1 Ag−1. The assembled symmetric supercapacitor device with HFPC-30 delivers a full-cell specific capacitance of ~457 Fg−1 in PVA-KOH hydrogel as gel electrolyte. A maximum specific energy of 25.3 Whkg−1 at ~4320 Wkg−1 specific power is obtained, which is very high compared to other reported carbon materials. Further, the assembled supercapacitor device works until 2V delivering a capacitance retention of ~85% after 10,000 cycles. Thus, biomass derived porous carbon material in a hydrogel electrolyte presents a novel strategy for developing highly promising sustainable electrodes for high energy, solid state supercapacitor applications. © 2021 Elsevier Ltd