<p>Rechargeable magnesium-ion batteries (RMBs) are emerging as attractive post-lithium-ion technologies due to their potential advantages in high energy density, intrinsic safety, economic viability, and resource sustainability. However, the advancement of magnesium batteries is hindered by the presence of a passivated film at the interface between the magnesium anode and electrolyte, as well as the slow diffusion kinetics of Mg²⁺. Therefore, designing RMBs electrolytes is considered an effective method to solve the above problems. This review provides a comprehensive analysis of advanced electrolyte design strategies for high-performance RMBs. It details the fundamental reaction mechanisms and existing challenges, including sluggish Mg²⁺ diffusion kinetics, irreversible anode passivation, narrow electrochemical windows, and corrosive/volatile components. This work systematically classifies and evaluates major electrolyte systems: Grignard reagents, Hexamethyldisilazide, Magnesium-Aluminum-Chloride Complex, boron-based salts, and ionic liquids. Key design principles for magnesium salts, solvents, and functional additives are discussed, emphasizing their roles in optimizing solvation structures, widening stability windows, suppressing passivation, enhancing ionic conductivity, and improving interfacial compatibility. The current progress in electrolyte development is briefly summarized, and future directions for magnesium batteries are outlined. This review offers insights into existing challenges and aims to inspire the design of commercially viable RMBs electrolytes.</p>