Biomass, which is derived from abundant renewable resources, is a promising alternative to fossil-fuel-based carbon materials for building a green and sustainable society. Biomass-based carbon materials (BCMs) with tailored hierarchical pore structures, large specific surface areas, and various surface functional groups have been extensively studied as energy and catalysis-related materials. This review provides insights from the perspectives of intrinsic physicochemical properties and structure-property relationships for discussing several fundamental yet significant issues in BCMs and their consequences. First, the synthesis, properties, and influencing factors of BCMs are discussed. Then, the causes and effects of the poor mechanical properties of biochar are explored. The factors affecting the properties of BCMs are presented, and the approaches for tuning these properties of biochar are summarized. Further, the applications of BCMs in energy storage and conversion are highlighted, including hydrogen storage and production, fuel cells, supercapacitors, hybrid electrodes, catalytic reforming, oxygen and CO2 reduction, and acetylene hydrochlorination. Finally, the future trends and prospects for biochar are proposed. This review aims to serve as a useful, up-to-date reference for future studies on BCMs for energy and catalytic applications.