The clean, green, and renewable energy source and its storage have attracted considerable interest from both industry and academia to address the ongoing global climate change. The waste biomass-derived porous carbon is an important research topic complementing its low-cost, eco-friendly, and renewable nature. Three-dimensional (3D) porous carbon was prepared by the one-step simultaneous carbonization and activation of natural lotus (Nelumbo nucifera) calyx. The as-prepared 3D-lotus calyx-derived activated carbon (3D-LCAC) electrode, with a specific surface area of 798 m2 g−1 delivered a remarkable specific capacitance of 223 F g−1 at 1 A g−1, with exceptionally high cycling stability, showing 97% retention of its initial capacitance, even after 50,000 charge-discharge cycles in a KOH electrolyte. It also demonstrated superior rate capability approximately 3-times higher than the commercial AC. The electrochemical performance of the 3D-LCAC electrode in a symmetric supercapacitor device was measured in aqueous (6 M KOH, 1 M Na2SO4) and ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) electrolytes. The ionic liquid electrolyte facilitated 3D-LCAC symmetric supercapacitor device delivered approximately ten-times higher energy density than that of aqueous electrolytes under similar electrochemical conditions. Overall, the 3D-LCAC from renewable and sustainable biowaste is a good candidate for high-performance electrode materials in practical supercapacitor applications.