<p>Biomass-derived activated carbon (AC) materials have become a research hotspot owing to their abundant sources. <i>Morchella esculenta</i> (ME) possesses a natural N, O self-doping and sponge-like structure, giving it the potential to form a nitrogen–oxygen-doped porous carbon structure. However, problems such as mildew and expiration occur during storage and transportation, resulting in resource wastage. In this study, waste ME serves as the raw material for fabricating ME-derived AC through KOH activation coupled with high-temperature carbonisation (MEAC-<i>T</i>-<i>x</i>). Systematic characterisation is carried out to decipher the electrochemical properties of MEAC-<i>T</i>-<i>x</i> in 1 M H₂SO₄ hydrous electrolytic medium. Results show that MEAC-700-4 exhibits a notable specific surface area of up to 2645.31 m² g^− 1, a hierarchically structured porosity encompassing micropores, mesopores and macropores, and a pronounced co-incorporation of N and O heteroatoms. The MEAC-700-4 sample, fabricated under ideal fabrication conditions, is chosen as the electrode material for supercapacitors. Moreover, the constructed symmetric supercapacitor system yields an elevated energy density of 13.44 Wh kg^− 1 under 250&#xa0;W kg^− 1 power density, outperforming most reported carbon-based supercapacitors. This work offers novel perspectives on the valorisation of biomass waste and the rational design of materials for supercapacitor electrodes with high electrochemical performance. Furthermore, the easy availability and low cost of waste ME, and the excellent electrochemical performance of MEAC-700-4 make ME-based supercapacitors promising for large-scale applications.</p><p></p>