Climate change and resource scarcity have intensified the global pursuit of sustainable, bio-based solutions, with macroalgae emerging as a promising yet underutilized resource. Within this context, this Doctoral Thesis explores the development of a novel cascade biorefinery framework for Furcellaria lumbricalis, a red macroalga abundantly available in the Baltic Sea region. The research is strictly linked to the principles of circular bioeconomy and aligns with the European Green Deal, EU Algae Strategy, and global sustainability agendas, addressing the need for innovative, low-impact, and resource-efficient biomass valorization pathways. The core objective of the thesis is to define and assess a life cycle sustainability assessment (LCSA) framework for an F. lumbricalis cascade biorefinery that integrates three key pillars of sustainability: environmental life cycle assessment (LCA), life cycle costing (LCC), and social life cycle assessment (S-LCA). This multidisciplinary and systems-based approach provides a holistic evaluation of the environmental performance, economic feasibility, and social impacts of multiple biorefinery design options. The novel cascade concept is designed to sequentially extract multiple high-value compounds, namely pigments, proteins, and carrageenan, while also valorizing residual biomass through energy recovery pathways or possible horticultural applications. Beyond addressing technical, environmental, and economic bottlenecks, the thesis emphasizes the underexplored social dimension of macroalgae-based biorefineries by implementing an original S-LCA framework tailored to the sector. This includes value chain hotspot analysis and community-level assessments of employment, stakeholder engagement, and regional development. The integration of these dimensions culminates in the development of a composite sustainability index using a multi-criteria decision-making method (TOPSIS), enabling the comparison of alternative biorefinery scenarios and the identification of the most sustainable configuration. The research methodology spans a comprehensive literature review compliant with PRISMA guidelines, detailed case study analysis in the Baltic Sea Region context, original data collection through the TACO ALGAE project, and model validation through peerreviewed scientific publications and international conferences. The findings underscore the scientific innovation of combining LCSA with macroalgal biorefinery design and highlight the practical significance of such systems for informing policy, guiding industry investments, and supporting sustainable marine bioresources management. By bridging technological development, environmental evaluation, and social implications, this Thesis provides a blueprint for scalable and replicable cascade biorefinery systems in Europe and beyond. It contributes a novel, transferable methodology for sustainability assessment in the marine bioeconomy and offers actionable insights for advancing F. lumbricalis as a cornerstone species in the emerging algae-based bio-industrial sector.