Single-atom catalysts (SACs) hold significant importance in catalysis due to their maximized atomic utilization efficiency, well-tuned active sites, and exceptional catalytic activity. However, their practical applications are hindered by the high cost of precursor materials and the complexity of sustainable synthesis. Biomass with diverse dimensions and chemical components has of potential to serve as a carbon substrate for the synthesis of high-performance SACs, which helps to promote the sustainable development for energy conversion, improve energy efficiency, and reduce environmental pollution. This review systematically introduces the synthesis methods, structure characterization techniques, and structure regulation strategies of biomass-based SACs (Bio-SACs). The recent advancements in Bio-SACs for energy conversion applications, including electrocatalysis, thermal catalysis, and photocatalysis, have been summarized. The challenges in the practical applications of Bio-SACs and the future research directions are highlighted with an emphasis on the impact of artificial intelligence (AI) and machine learning (ML) technologies in the design and fabrication of high-performance Bio-SACs.