Incorporation of pseudocapacitive materials into porous carbon is a promising strategy to boost electrochemical performance. Herein, composite of biomass-derived porous carbon and MnO2 (a typical pseudocapacitive material) was facilely fabricated through an in-situ synthesis approach with sorghum seeds derived porous carbon (SSC) as the skeleton for MnO2 deposition. The as-prepared composite ( MnO2@SSC) exhibits hierarchical porous structure with abundant interlaced MnO2 nanowires wrapping on the surface. While the porous structure is beneficial to the active sites exposure and electrolyte ions transport, the interlaced three-dimensional (3D) network of MnO2 nanowires significantly boosts the tolerance toward volume shrinkage/expansion during the cyclic process. Consequently, the MnO2@ SSC-based electrode delivered quite promising supercapacitive performance including superior specific capacitance of 482.7 F/g at 0.5 A/g, outstanding long-term cycling stability (95.8% specific capacitance retention after 20,000 cycles) and high energy density of 13.7 Wh/kg at power density of 298.1 W/kg. Furthermore, all-solid-state flexible supercapacitor based on MnO2@ SSC can be facilely bent to various angles (0° to 150°) without significant degradation in the capacitive performance. This study provides a facile, cost-effective, and sustainable approach for the fabrication of high-performance electrode materials.