Catalytic transformation of CO₂ into high-value chemicals and fuels has been considered as one of the most forceful approaches because it offers an alternative to fossil energy and the benefit of transforming and utilizing the excessive CO₂ emission on a grand scale. However, owing to the high chemical inertness of CO₂ and the complexity of reaction systems, developing efficient catalysts for selective CO₂ conversion remains challenging. Single-atom catalysts (SACs), which offer maximum atomic utilization, well-defined active sites, and controllable supports, which have presented growing significance for CO₂ utilization with multiple methods have been developed enhance performances their performance. Herein, this review comprehensively summarizes the latest breakthroughs in microenvironment engineering of isolated atomic sites through a systematic comparison in terms of design principles, synthetic methods, characterization techniques, and the theoretical understanding of correlations between structure and performance of state-of-the-art SACs in hydrogen production and CO₂ conversion. Subsequently, recent progress in several typical hydrogen production and CO₂ conversion are investigated to receive in-depth understanding of the catalytic mechanisms over finely-modulated SACs. Finally, challenges and future perspectives for the design of SACs are presented. This review will offer new insights into developing SAC materials for hydrogen production and CO₂ conversion and will ultimately contribute to achieving carbon neutrality.