The doping of metallic impurities into hydrated oxide structures is a suitable strategy to enhance the pseudocapacitive storage and improve the strength of electrode materials. In this work, we have prepared Mg-doped WO3·H2O nanoplates via a facile one-step wet-chemical synthesis route. The doping of Mg2+ ions effectively improved the electrical conductivity, electroactive sites, and ion diffusion kinetics of WO3·H2O while maintaining its layered hydrated structure. The rational doping of Mg in hydrated tungsten oxide (WOM5, ∼3% Mg doping) electrodes exhibited superior specific capacitance (158 F g-1 at 1 A g-1) behavior with higher b-values (0.82), enhanced redox activity, and improved charge storage kinetics than other compositions. Furthermore, the fabricated aqueous asymmetric device demonstrated excellent long-term cycling stability with improved coulombic efficiency up to 5,000 cycles. These results highlight Mg doping as an effective strategy for enhancing the electrochemical performance and stability of WO3·H2O-based supercapacitors.