The trend in the scientific community is the fabrication of porous activated carbon from the waste material for energy storage applications. In this regard, this is our first attempt to synthesize N-doped porous activated carbon derived from poultry waste (PW) for the fabrication of a flexible supercapacitor. The specific capacitance proliferated 7.2 times after chemical activation with KOH. After activation of PW material, the energy density of symmetric supercapacitor snowballed significantly from 16 to 23 Wh/kg. In addition, the durability of the supercapacitor enhanced from 83 to 99% after activation. The enhancement in the specific capacitance and energy density was noted after the activation process due to the high surface area of PW-derived carbon by activation with KOH. The enhancement in cycle life has been observed due to the high degree of graphitization. Moreover, an all-solid-state flexible supercapacitor (ASSFSC) fabricated using N-doped activated carbon showed an enormous energy density of 21.5 Wh/kg. The results demonstrate that the supercapacitor fabricated using activated PW-derived carbon could be commercialized easily.