Abstract: To align with the “dual carbon” goals and address the inherent limitations of direct pyrolysis biochar—such as low specific surface area, insufficient surface functional groups, and constrained high-value applications—the fabrication techniques and electrochemical applications of biomass-derived nitrogen-doped porous carbon are systematically examined, providing theoretical support for its tailored design and industrial-scale production. Based on the classification of nitrogen-rich and nitrogen-poor biomass precursors, the mechanisms and effectiveness of physical and chemical activation are compared. The process characteristics of one-step methods （simultaneous pyrolysis, activation, and doping） and multi-step methods （sequential pyrolysis, activation, and doping） are systematically analyzed. Furthermore, the structure–performance relationships between hierarchical pore structures, nitrogen doping features （including the types and contents of nitrogen-containing functional groups）, and electrochemical properties are thoroughly discussed, with special emphasis on the application mechanisms in supercapacitors, oxygen reduction reaction （ORR） electrocatalysis, and lithium-/sodium-ion batteries. Results indicate that chemical activation, particularly with KOH, outperforms physical activation in constructing high specific surface areas （up to 3142 m²/g） and hierarchical porous structures. Nitrogen-rich biomass can achieve a nitrogen content as high as 19.45% via self-doping, whereas nitrogen-poor biomass requires external nitrogen sources. Although the one-step method is more efficient, it faces a fundamental trade-off between enhanced high-temperature activation and reduced nitrogen retention. Fast pyrolysis technology emerges as a promising approach for the synergistic regulation of pore structure and nitrogen content. Owing to their hierarchical porosity and abundant nitrogen-containing functional groups, these materials exhibit a maximum specific capacitance of 473.5 F/g with 99% cycling retention in supercapacitors, demonstrate ORR activity and stability comparable to those of commercial Pt/C, and significantly improve ion storage and transport in secondary batteries. In summary, the synergistic modification through activation and nitrogen doping is crucial for optimizing biochar performance. The one-step method represents a primary direction for future low-cost production. Subsequent research should focus on optimizing process parameters, elucidating reaction mechanisms, and ensuring batch consistency to facilitate large-scale application in electrochemical energy storage and conversion.