<p>Spinel-type MgCo₂O₄ has gained recognition as a viable choice for pseudocapacitive power storage due to its rich redox chemistry and structural stability. Nevertheless, its real-world application is limited by moderate conductance and limited surface reactivity. To overcome these limitations, we synthesized a ternary hybrid nanocomposite comprising MgCo₂O₄ and MgO integrated with multiwalled carbon nanotubes (MWCNTs), yielding a MgCo₂O₄/MgO@MWCNT (MMM) composite engineered as the cathode in an asymmetric capacitor system. The incorporation of MgO promotes electrochemical hydration, improving OH⁻ ion accessibility, while MWCNTs provide a conductive and porous scaffold that facilitates accelerated electron transfer and ion mobility. Electrochemical evaluations in a three-electrode arrangement reveal a high specific capacitance of 1640 F g⁻¹ at 1 A g⁻¹, along with superior rate performance and redox reversibility. When assembled with activated carbon (AC) as the anode, the ASC device provides a highest energy density of 47.08 Wh kg⁻¹ at 748.6 W kg⁻¹, maintaining 93% of its initial capacitance over 10,000 cycles with nearly 99% coulombic efficiency. The better electrochemical behaviour can be ascribed to the synergistic interaction of MgCo₂O₄’s multiple redox transitions, MgO’s surface reactivity, and the conductive framework of MWCNTs. This work underscores the potential of MMM composites in developing high-performance, long-life supercapacitors for advanced energy storage technologies.</p>