This study aims to contribute to the sustainable development of blue growth in Europe via cascade biorefineries of native seaweed bioresources by investigating the economic viability and environmental sustainability of three conceptual macroalgal biorefinery systems that utilize endemic brown macroalgae Laminaria digitata, Fucus vesiculosus, and Saccharina latissima. The present study conceptualised lab and pilot scale demonstration trials conducted in the MAB4 research project as fully operational biorefinery systems producing food-grade fucoidan and laminarin via sequential extraction and producing feed supplement via side-stream valorisation. The economic analysis of the base case scenario (Part I) identified the membrane use and extraction efficiency as two critical techno-economic barriers for the biorefinery systems. In the improved technology scenarios (Part II), all systems demonstrated promising economic potentials. Over a 15-year project span, pilot scale systems (2–7 metric tons (t) dry matter (dm) feedstock/year) and industrial scale systems (900 t dm/year) obtained a net present value (NPV) of 20–506 k EUR and 186–454 Mio EUR, respectively. Feedstock costs and laminarin and fucoidan sales are the major cost and revenue drivers. A sensitivity analysis of the economic viability of industrial scale systems (Part III) identified the break-even price of 33, 52, and 67 EUR/kg dm feedstock for the F. vesiculosus, S. latissima, and L. digitata system, respectively. The net carbon footprint and net water footprint of the industrial scale systems range from 3.8 to 11 kg CO2eq./kg dm feedstock and from 0.1 to 0.2 m3 water/kg dm feedstock, respectively. Onsite energy consumption for product drying and process heating and the upstream energy use for membrane manufacturing dominate the system-level carbon footprints, with a respective share of 37–70% and 8–61%. Further development towards environmental sustainability can be achieved by internal process and system optimizations and externally by greening the electricity mix.