A high-performance all-inorganic magnesium–lithium chloride complex (MLCC) electrolyte is synthesized by a simple room-temperature reaction of LiCl with MgCl₂ in tetrahydrofuran (THF) solvent. Molecular dynamics simulation, density functional theory calculation, Raman spectroscopy, and nuclear magnetic resonance spectroscopy reveal that the formation of [Mg_xLi_yCl_2x+y·nTHF] complex solvation structure significantly lowers the coordination number of THF in the first solvation sheath of Mg²⁺, which significantly enhances its de-solvation kinetics. The MLCC electrolyte presents a stable electrochemical window up to 3.1 V (vs Mg/Mg²⁺) and enables reversible cycling of Mg metal deposition/stripping with an outstanding Coulombic efficiency up to 99% at current densities as high as 10 mA cm⁻². Utilizing the MLCC electrolyte, a Mg/Mo₆S₈ full cell can be cycled for over 10000 cycles with a superior capacity retention of 85 mA h g⁻¹ under an ultrahigh rate of 50 C (1 C = 128.8 mA g⁻¹). The facile synthesis of high-performance MLCC electrolyte provides a promising solution for future practical magnesium batteries.