Display omitted •KMnO4 is used as activating agent and template precursor during pyrolysis process.•Hierarchical porous carbon shows high gravimetric capacitances.•The symmetric device shows high energy density and good electrochemical stability. Hierarchical porous carbon materials exhibit huge potential in high performance supercapacitors. Nevertheless, developing a convenient and sustainable approach remains a big challenge. Herein, we report a novel approach for synthesis of heteroatoms-doped hierarchical porous carbon derived from chitin using KMnO4 as activating agent and template precursor with amidogen and hydroxyl assist. The formation and evolution process of the hierarchical porous carbon are researched in detail. The optimized hierarchical porous carbon materials (HPC-700) have large specific surface area, hierarchical porous framework and numerous nitrogen and oxygen functional groups. As a result, the HPC-700 electrode displays an ultrahigh specific capacitance of 412.5 F g−1 at 0.5 A g−1, good rate characteristic and remarkable electrochemical stability (only 0.4% loss after 10,000 cycles). Significantly, the constructed flexible all-solid-state symmetric supercapacitor shows a high energy density of 9.67 Wh Kg−1 and superior electrochemical stabilization in PVA/KOH sol electrolyte. The research highlights a new, convenient approach for construction of hierarchical porous carbon materials for supercapacitors.