Photocatalysis driven by solar energy is a feasible strategy to alleviate energy crises and environmental problems. In recent years, significant progress has been made in developing advanced photocatalysts for efficient solar‐to‐chemical energy conversion. Single‐atom catalysts have the advantages of highly dispersed active sites, maximum atomic utilization, unique coordination environment, and electronic structure, which have become a research hotspot in heterogeneous photocatalysis. This paper introduces the potential supports, preparation, and characterization methods of single‐atom photocatalysts in detail. Subsequently, the fascinating effects of single‐atom photocatalysts on three critical steps of photocatalysis (the absorption of incident light to produce electron‐hole pairs, carrier separation and migration, and interface reactions) are analyzed. At the same time, the applications of single‐atom photocatalysts in energy conversion and environmental protection (CO2 reduction, water splitting, N2 fixation, organic macromolecule reforming, air pollutant removal, and water pollutant degradation) are systematically summarized. Finally, the opportunities and challenges of single‐atom catalysts in heterogeneous photocatalysis are discussed. It is hoped that this work can provide insights into the design, synthesis, and application of single‐atom photocatalysts and promote the development of high‐performance photocatalytic systems. Single‐atom catalysts (SACs) have the maximum atomic utilization, unique coordination environment, and electronic structure, which make them exhibit fascinating performance in the field of heterogeneous photocatalysis. This review summarizes the potential support, preparation, and characterization techniques of SACs. Notably, the unique properties of SACs in photocatalytic reaction and its latest research progress in energy conversion and environmental protection are discussed.