In this work, we reported a moss-derived biomass porous carbon (MPC) as a bi-functional electrode material for both the lithium–sulfur battery and the supercapacitor. The MPC was prepared from a high-temperature calcination procedure using the moss as the carbonaceous precursor. Using NaOH, the MPC was activated to give a mesoporous structure with a high specific surface area (1057.1 m2 g−1) and large pore volume (0.72 cm3 g−1). When it was used as the cathode material in lithium–sulfur batteries, the MPC material realized a sulfur loading and exhibited a remarkably improved electrochemical performance, i.e., a high discharge capacity of 1070 mAh g−1 at 0.1 C. This activated MPC also worked well as a capacitive electrode in supercapacitors, demonstrating a high specific capacitance of 332 F g−1 (scan rate of 1.0 A g−1) and a high capacity retention > 97% in a long-term cycle of 1000 charge/discharges. This work demonstrated a facile method for the utilization of activated waste biomass material for future clean energy applications.