Oxidative stress is a critical factor contributing to the pathogenesis of numerous diseases, including cardiovascular disorders, diabetes, and neurodegenerative conditions. In recent years, marine-derived antioxidants have emerged as promising therapeutic agents due to their unique biological activities and diverse sources. This comprehensive review explores the therapeutic potential of various marine antioxidants in mitigating oxidative stress-associated diseases. Marine organisms are rich in bioactive compounds, such as polysaccharides, polyphenols, carotenoids, peptides, and vitamins, which exhibit potent antioxidant and free radical scavenging abilities. These compounds have been shown to effectively inhibit oxidative reactions, repair oxidative damage, and enhance the body's antioxidant defense mechanisms. For instance, marine polysaccharides and their derivatives can scavenge reactive oxygen species (ROS), protect neurons from oxidative damage, and alleviate inflammation in neurodegenerative diseases like Alzheimer's and Parkinson's diseases. Similarly, marine unsaturated fatty acids, such as omega-3 polyunsaturated fatty acids (PUFAs), have been found to reduce cardiovascular risks by lowering serum triglyceride levels and improving vascular endothelial function. Additionally, marine-derived superoxide dismutase (SOD) plays a crucial role in neutralizing ROS, thereby offering protection against oxidative stress in various diseases. Despite these promising findings, challenges remain in the field, including the need for improved extraction and purification technologies, more comprehensive activity evaluation systems, and further research into the safety and bioavailability of these compounds. This review provides a detailed overview of the current research status, highlighting the types, structural characteristics, antioxidant activities, and mechanisms of action of marine antioxidants. It also identifies key areas for future research and development, aiming to harness the full potential of marine-derived antioxidants in the prevention and treatment of oxidative stress-related diseases.