Marine macroalgae are versatile third-generation biomass with significant potential to produce high-value bioactive compounds such as pigments, rare sugars, sulfated polysaccharides, and oligosaccharides, which are increasingly relevant for pharmaceutical, nutraceutical, and cosmetic applications. This review hypothesizes that a comprehensive understanding of both well-established and emerging bioactive compounds, along with improvements in extraction methodologies, is essential for realizing the full potential of macroalgae-based biorefineries. Unlike previous studies, this review uniquely consolidates underexplored bioactives and emerging extraction strategies, thereby offering a roadmap for biorefinery development. The contribution of this work lies in identifying critical bottlenecks in macroalgal valorization and presenting integrated biorefinery strategies tailored for sustainable adoption. With the global demand for marine-derived ingredients projected to reach approximately USD 16 billion by 2030, this review highlights commercially viable compounds, eco-efficient extraction routes, and future directions such as the integration of omics technologies, bioprocess intensification, and valorization of underutilized species. The significance of this review lies in highlighting that eco-efficient extraction methods, particularly those using green solvents and process intensification, are the most promising for scalability. Moreover, rare sugars, pigments, and sulfated oligosaccharides remain commercially underexploited yet hold high potential. Addressing biomass variability and economic constraints requires integrated biorefinery strategies. By offering a holistic and forward-looking perspective, this review bridges existing knowledge gaps and provides strategic insights into the future development of sustainable marine macroalgal utilization for high-value industrial applications.