Atherosclerotic cardiovascular disease (ASCVD) remains a leading cause of morbidity and mortality worldwide, driven by dyslipidemia, chronic inflammation, oxidative stress, and endothelial dysfunction. Despite widespread use of lipid-lowering and anti-inflammatory agents such as statins, residual cardiovascular risk and adverse effects underscore the need for novel, safe, and multi-targeted therapies. Marine-derived polysaccharides (MDPs)-including fucoidan, alginate, laminarin, carrageenan, and chitosan-exhibit a spectrum of bioactivities relevant to ASCVD pathogenesis, such as anti-inflammatory, antioxidant, lipid-modulatory, antithrombotic, and endothelial-protective effects. In this critical review, we synthesize preclinical and emerging clinical evidence on the pharmacokinetics, mechanisms of action, and therapeutic potential of these compounds. We highlight translational challenges, including structural variability, poor oral bioavailability, and limited human data, and propose strategies to overcome these barriers, such as molecular standardization, novel delivery systems, and well-designed clinical trials. MDPs represent promising natural therapeutics for ASCVD prevention and treatment, warranting further investigation in rigorous human studies.