Baijiu distillers’ grains (BDGs, Jiuzao) are produced in large quantities by China’s solid-state Baijiu industry and remain largely underutilized. BDGs retain substantial levels of dietary fibers, proteins and peptides, phenolic compounds, and fermentation-derived metabolites. This review summarizes recent advances in the recovery, structural characterization, and functional evaluation of BDG-derived components, with particular emphasis on non-starch polysaccharides as the core functional fraction. We discuss how solid-state fermentation and processing conditions influence the structural features of arabinoxylan-rich polysaccharides, polysaccharide–protein associations, and feruloylated motifs, and how these characteristics relate to reported antioxidant activity, gut microbiota modulation, immunoregulatory effects, and prebiotic fermentation behavior. Beyond isolated fractions, growing evidence highlights the importance of matrix-level interactions among polysaccharides, peptides, and phenolics in shaping functionality within complex food systems. In parallel, emerging application opportunities in functional foods, nutraceutical formulations, biomaterials, and cascade utilization frameworks are summarized from a sustainable processing perspective. Finally, key challenges for industrial translation are identified, including batch variability, structure–function standardization, scalable and food-grade processing, safety evaluation, and regulatory considerations.