<p>Biomass-derived activated carbon (AC) from Mahogany seed shells (MSS) was successfully synthesized and modified with carbon nanotubes (CNTs) through chemical and physical activation processes that are reproducible to apply as high-performance supercapacitor electrodes. Various additions of CNT (2%, 4%, 8%, and 10% of the mass of 30 g of activated carbon) were made during the chemical activation stage to evaluate their effects on the structural and electrochemical properties of the material, which were then coded as MSS-02, MSS-04, MSS-08, and MSS-10, respectively. The results showed that increasing the percentage of CNTs increased the crystallinity and promoted the formation of conductive nanotube networks on the porous carbon surface. The specific surface areas ranged from 422 to 594 m²/g, with 2.3–3.9 nm pore diameters, indicating a well-developed mesoporous structure. Electrochemical tests in 1 M H₂SO₄ electrolyte showed that the MSS-08 provided the highest specific capacitance of 366 F/g, and energy and power density of 50 Wh/kg and 183 W/kg, respectively. The improved electrochemical performance was due to the synergistic effect of CNTs, which could increase electrical conductivity, accelerate electron and ion transport, and maintain structural stability during charge and discharge cycles. In addition, the improved wettability and connectivity of the CNT network allowed more active sites to be accessible to ions, thereby enhancing ion diffusion and charge storage capacity. Based on these results, AC-MSS modified CNTs are a promising and sustainable electrode material candidate for high-performance supercapacitor applications.</p>