This study introduces monolithic three-dimensional nanoporous magnesium (3D-NPMg) fabricated through a scalable solution-based dealloying process as electrodes. By employing a naphthalene-based reductive environment, this approach forms a hierarchically porous 3D structure with clean metallic surfaces, thereby forming a free-standing 3D bicontinuous nanostructure. The resulting 3D-NPMg addresses critical challenges in magnesium metal battery (MMB) anodes, including high polarization, dendritic growth, and limited cycling stability. Electrochemical performance tests show that 3D-NPMg exhibits lower overpotentials, improved charge-transfer kinetics, and a significantly extended cycling life. The interconnected porous structure facilitates efficient ionic transport and uniform Mg deposition, thus suppressing volume expansion and reducing top-plating during cycling. With its rapid oxidation-minimizing synthesis, this solution-based dealloying process offers broad applications across various metals, which can advance the development of stable, high-performance anodes for next-generation MMBs.