Bagasse-derived carbon electrodes were developed by doping with nitrogen functional groups and compositing with high-capacity MnO₂ nanoparticles (MnO₂/NBGC). The bagasse-derived biochar was N-doped by refluxing in urea, followed by the deposition of MnO₂ nanoparticles onto its porous surface via the hydrothermal reduction of KMnO₄. Different initial KMnO₄ loading concentrations (i.e. 5, 10, 40, and 100 mM) were applied to optimize the composite morphology and the corresponding electrochemical performance. Material characterization confirmed that the carbon composite has a mesoporous structure along with the dispersion of MnO₂ nano-particles on the N-containing carbon surface. It was found that the 5-MnO₂/NBGC sample exhibited the highest electrochemical performance with a reversible capacity of 760 mA h g⁻¹ at a current density of 186 mA g⁻¹. It delivered reversible capacities of 488 and 390 mA h g⁻¹ in cycle tests at 372 and 744 mA g⁻¹, respectively, for 150 cycles and presented good reversibility with nearly 100% coulombic efficiency. In addition, it could exert high capacities up to 388 and 301 mA h g⁻¹ even under high current densities of 1860 and 3720 mA g⁻¹, respectively. Moreover, most of the prepared composite products showed high rate capability with great reversibility up to more than 90% after testing at a high current density of 3720 mA g⁻¹. The great electrochemical performance of the MnO₂/NBGC nanocomposite electrode can be attributed to the synergistic impact of the hierarchical architecture of the MnO₂ nanocrystals deposited on porous carbon and the capacitive effect of the N-containing defects within the carbon material. The nanostructure of the MnO₂ particles deposited on porous carbon limits its large volume change during cycling and promotes good adhesion of MnO₂ nanoparticles with the substrate. Meanwhile, the capacitive effect of the exposed N-functional groups enables fast ionic conduction and reduces interfacial resistance at the electrode interface.