<p>This study reports on the valorization of <i>Hyparrhenia hirta</i> (biowaste) into a valuable electrode material for high-performance supercapacitor applications. Biowaste-derived activated carbons (ACs) with a tailorable porous texture are attained via a two-step process. Hence, a hydrothermally and microwave-irradiated (HSW) carbon shows a meso/microporous texture with a specific surface area of ~ 991 m²&#xa0;g⁻¹ and a pore size of 3.09&#xa0;nm in diameter. The HSW electrode exhibits the highest specific capacitance (Cs) of ~ 501.6 F/g at 2 A/g in 1&#xa0;M Na₂SO₄ aqueous electrolyte (three-electrode configuration), with an outstanding cyclability of 84.6% over 10,000 charge/discharge cycles at 10 A/g. A fabricated aqueous symmetric supercapacitor shows the highest specific capacitance of 106.6 F/g at 2 A/g in 1&#xa0;M Na₂SO₄ aqueous solution, with the highest energy density of 33.3 W h/kg at a power density of 1500 W/kg. Further, a solid-state symmetric supercapacitor using a PVA/ Na₂SO₄ gel electrolyte exhibits <i>Cs</i> ~ 101.9 F/g at 2 A/g with a high energy density of ~ 31.8 W h/kg at a power density of ~ 1200 W/kg, as well as excellent cyclability up to 10,000 cycles. The auspicious outcomes strongly ensure a high possibility of eco-friendly electrode materials for supercapacitor applications.</p> Graphical Abstract <p></p>