The conventional methods of producing metallic magnesium involve high temperatures, high pollution, and high energy consumption. Herein, the separation and production of metallic magnesium from salt lake brine was carried out using an environmentally friendly extraction-electrodeposition method. 16 functional ionic liquids, consisting of four saponified anions and four quaternary ammonium salt cations, were synthesized and employed as both extractants and supporting electrolytes. The study showed that the compound [A336][V10], which was produced using methyltrioctylammonium ([A336]+) and saponified neodecanoic acid ([V10]−), exhibited a significant extraction rate of Mg2+ and electrical conductivity in methyl isobutyl ketone (MIBK). The extraction efficiency for Mg2+ with a concentration of 54.04 g·L−1 was found to be 60.98%. After extraction, the electrical conductivity of the organic phase was measured to be 649 μS·cm−1. The extraction mechanism and phase equilibria showed that the organic system exhibited limited solubility with the aqueous phase, and the Mg2+ in the brine was extracted by [A336][V10] in the form of MgCl2·2[A336][V10] through monodentate coordination with the carboxyl group in [V10]−. Following extraction, metallic magnesium was successfully electrodeposited from the organic phase. This is the first time that metallic magnesium was directly produced from a common extraction system at room temperature. This method avoids both the dehydration of MgCl2·6H2O and the melting of anhydrous MgCl2 at high temperatures, which are typically encountered in the traditional procedure of producing metallic magnesium from brines, and it offers a new strategy for metallic magnesium production with low energy consumption.