<p>MnPO₄∙H₂O is an ideal precursor for the preparation of LiMnPO₄. However, the instability of Mn³⁺ in an aqueous solution necessitates the implementation of the existing preparation methods, which are carried out in ethanol and produce toxic gases such as NO and NO₂. In this work, a radical-oxidation coupled phosphate stabilization strategy is proposed for synthesizing MnPO₄∙H₂O in an aqueous solution. The strategy involves the initial oxidation of Mn²⁺ to Mn³⁺ by sulfate radicals, which are produced through the thermal activation of Na₂S₂O₈. Subsequently, Mn³⁺ is stabilized by H₃PO₄, leading to the formation of MnPO₄∙H₂O. By implementing this strategy, the mesoporous MnPO₄∙H₂O precursor can be readily obtained through a reaction at 90&#xa0;°C for 5&#xa0;h. Subsequently, the prepared LiMnPO₄/C inherits the mesoporous structure of the MnPO₄∙H₂O precursor, exhibiting excellent electrochemical performance. Specifically, the mesoporous LiMnPO₄/C delivers an initial capacity of 115.8 mAh g⁻¹ with a capacity retention of 83.1% after 100 cycles at 10&#xa0;C. The enhanced performance is mainly attributed to the mesoporous structure, which facilitates electrolyte penetration, reduces interfacial charge transfer impedance, and accelerates Li⁺ diffusion. The environmentally benign and scalable strategy presented here opens a new approach to the synthesis of high-performance LiMnPO₄/C.</p>