Despite the exceptionally large theoretical energy density of lithium–oxygen batteries, their high charging overpotential and poor cycle life are critical limitations preventing their commercialization. To overcome these bottlenecks, redox mediators (i.e., soluble catalysts) that facilitate the electrochemical reaction between lithium and oxygen have attracted tremendous research interest. A wide variety of materials have been reported as promising redox mediators for lithium–oxygen batteries, successfully enhancing energy efficiency and cycle stability. However, their overall performance still requires further improvement. Herein, recent progress on the use of redox mediators for lithium–oxygen batteries are reviewed, with a particular focus on improvements in energy efficiency, power capability, and coulombic efficiency. In addition, the aspects of redox mediators requiring immediate optimization are discussed together with future research directions.