Marine polysaccharides have emerged as promising candidates in theranostic applications due to their unique physicochemical and biological properties. These biopolymers, derived from marine organisms such as algae, crustaceans, and microorganisms, offer biocompatibility, biodegradability, and bioactivity, making them suitable for a range of biomedical applications. Their ability to form hydrogels, films, and nanostructures enhances their utility in drug delivery systems, tissue engineering, and wound healing. The integration of marine polysaccharides in theranostic applications is driven by their multifunctional capabilities, including therapeutic efficacy and diagnostic potential. While marine polysaccharides hold significant promise in theranostic applications, challenges remain in optimising their properties for specific uses. The variability in polysaccharide characteristics based on their marine source and extraction methods can affect their performance. Additionally, further research is needed to fully understand their interactions with biological systems and to develop standardised protocols for their use in clinical settings. Despite these challenges, the potential of marine polysaccharides in theranostics continues to drive research and innovation in the field.