Biomass-derived carbon materials are receiving much attention for supercapacitor applications due to their well-developed porous structures, large specific surface areas, good conductivity, and environmental sustainability. In this study, we present a simple and scalable green strategy to prepare nitrogen (N)-doped biocarbon materials from naturally decayed wood (rotten wood, RW), which is to take advantage of the intrinsic porous nature of wood and the structural modifications induced by microbial activation (e.g., surface oxidation and nitrogen incorporation). To further increase the doped nitrogen content, we used aqueous ethylenediamine (EDA) solution for activating and immersing pre-treated RW. The N-doped biocarbon samples show uniform nitrogen distribution and favorable graphitization, resulting in outstanding supercapacitor performance. The optimized sample, RW-1000, exhibits a high specific surface area of 1204 m 2·g -1 with a rational pore structure. When applied as a supercapacitor electrode, RW-1000 demonstrates excellent electrochemical properties, including a specific capacitance of 448 F·g -1 at 0.2 A·g -1 and remarkable stability, retaining 95% of its capacitance after 10,000 cycles. This exceptional energy storage performance is attributed to the RW-1000-derived electrode’s high specific surface area, optimal pore size distribution, and well-dispersed nitrogen content. Thus, our work offers a sustainable, scalable and facile strategy for transforming biomass waste into valuable biocarbon materials for high performance supercapacitors.