Abstract: Solvent extraction, a separation and purification technology, is crucial in critical metal metallurgy. Organic solvents commonly used in solvent extraction exhibit disadvantages, such as high volatility, high toxicity, and flammability, causing a spectrum of hazards to human health and environmental safety. Neoteric solvents have been recognized as potential alternatives to these harmful organic solvents. In the past two decades, several neoteric solvents have been proposed, including ionic liquids (ILs) and deep eutectic solvents (DESs). DESs have gradually become the focus of green solvents owing to several advantages, namely, low toxicity, degradability, and low cost. In this critical review, their classification, formation mechanisms, preparation methods, characterization technologies, and special physicochemical properties based on the most recent advancements in research have been systematically described. Subsequently, the major separation and purification applications of DESs in critical metal metallurgy were comprehensively summarized. Finally, future opportunities and challenges of DESs were explored in the current research area. In conclusion, this review provides valuable insights for improving our overall understanding of DESs, and it holds important potential for expanding separation and purification applications in critical metal metallurgy.