Sustainable development of membrane technologies requires novel source materials for membrane production which are not fossil fuel derived and do not use petroleum solvents for their fabrication. Here, we demonstrate eco-friendly and straightforward manufacturing of thin-film composite (TFC) membranes using crude soluble algal biomass without the need for chemical purification. Both sterilized clean-water and unsterilized wastewater-grown green algal biomasses generated similar results. The complex mixture of polysaccharides and soluble proteins provided reactive groups for crosslinking. The thickness of the selective layer made of algal biomass ranged from 13 to 94 nm. The algae-based TFC membranes exhibited robust stability in long-term tests performed in a continuous crossflow filtration system for 7 days. The sustainability and economic efficiency of our algal TFC membranes were compared to the state-of-the-art membrane fabrication and demonstrate, for the first time, that crude biomass, without excessive purification of bio-monomers or -polymers, can be successfully upcycled into membrane separation materials. The results provide a novel venue for conversion of algal biomasses that may not be suited for other consumer-use avenues like those produced from genetically modified strains or in wastewaters, into a useful material.