The flexible all-solid-state supercapacitors based on faidherbia albida fruit shell derived activated carbon and MnO2/faidherbia albida fruit shell derived carbon as electrodes and PVA-KOH gel as electrolyte is synthesized. MnO2 nanowire-like structure is grafted on the faidherbia albida fruit shell-derived activated carbon via a hydrothermal synthesis method. The microstructures of the as-prepared materials are characterized by scanning electron microscopy, nitrogen adsorption/desorption isotherms, X-ray diffraction, Raman spectra and X-ray photoelectron spectroscopy techniques. Due to the synergistic effects between MnO2 and waste biomass derived carbon, the MnO2/faidherbia albida fruit shell-derived carbon hybrid composite electrode presents satisfactory electrochemical performance with high specific capacitances of 426 F g−1 and 202.5 F g−1 in two different electrolytes such as 3.0 M KOH and 1.0 M Na2SO4, respectively. Furthermore, benefiting from the combination of a high specific surface area of obtained activated carbon and high specific capacitance of MnO2, an all-solid-state asymmetric supercapacitor exhibits a high energy density of 32 Wh kg−1 at a power density of 400 W kg−1 in the voltage range of >1.6 V, which demonstrate that the synthesized MnO2/biomass-derived activated carbon hybrid composite with unique structure has considerable potential in flexible all-solid-state supercapacitors.