Marine bioresources, owing to their unique metabolic adaptation mechanisms, contain an abundance of bioactive constituents that may aid in the prevention and intervention of obesity and its metabolic complications. This study systematically elucidates the chemical structural characteristics and sources of four major categories of marine-derived anti-obesity bioactive substances, namely, marine polysaccharides, lipids, protein-derived peptides, and polyphenols and natural pigments. Using structure–function relationships as the guiding framework, the intrinsic links between key structural elements and anti-obesity effects were outlined. Based on this, existing research evidence has been consolidated to provide an overview of the synergistic action of these substances, achieved through multiple pathways. These include influencing adipocyte differentiation and lipid synthesis, promoting fatty acid oxidation and energy expenditure, alleviating chronic inflammation and oxidative stress through the regulation of lipid digestion, absorption, and transport, and participating in the regulation of host energy homeostasis via the gut microbiota and their metabolites. Lastly, focusing on translational applications, this study summarizes the status of development of marine-derived antiobesity functional foods and dietary supplements and proposes that food-grade processing and delivery strategies can be adopted to improve the reproducibility and practical feasibility of the observed effects. The findings of this review can serve as a reference for the high-value utilization of marine resources and development of anti-obesity products.