| Marine green macroalgae of the genus Ulva (Chlorophyta) have gained increasing scientific interest due to their high nutritional profile and abundance of biologically active constituents. Among these, ulvan—a sulfated polysaccharide predominantly found in the cell walls of Ulva species—represents the principal water-soluble dietary fiber with extensive pharmacological relevance. Ulvan is recognized for its multifaceted bioactivities, including immunomodulatory, antioxidant, antiviral, anticancer, and antihyperlipidemic effects. These biological functions are largely attributed to its unique structural features, such as sulfate content, monosaccharide composition, and molecular conformation, which enable interactions with diverse molecular targets and modulation of cellular signaling pathways across plant and animal systems. In addition to its health-promoting properties, ulvan contributes significantly to gastrointestinal health by enhancing fiber intake, thereby playing a preventive role against chronic diseases such as cardiovascular disorders and metabolic syndromes. Owing to its broad bioactivity and favorable physicochemical characteristics, ulvan is considered a promising candidate for applications in nutraceuticals, pharmaceutical formulations, agricultural biostimulants, and sustainable biomaterials. This review presents a comprehensive analysis of recent advancements in extraction and purification strategies for ulvan, emphasizing the utility of acid-assisted methods, membrane filtration techniques, and advanced analytical platforms for profiling sugar composition and molecular weight. Furthermore, the review critically evaluates experimental evidence on the therapeutic and functional potential of ulvan, highlighting its versatility as a biopolymer with significant translational potential across multiple industrial domains.