Water scarcity remains a critical global challenge, necessitating the advancement of sustainable water treatment technologies. Polymeric membranes have emerged as an indispensable solution for desalination and wastewater treatment due to their high efficiency and low energy consumption. However, conventional membrane fabrication relies on petroleum-derived polymers and toxic solvents, generating significant environmental concerns. This review sheds light on the state-of-the-art approaches to sustainable membrane development, focusing on green chemistry principles and circular economy strategies. Mechanosynthesis offers a solvent-free alternative for synthesizing advanced membrane materials, including metal-organic frameworks, covalent organic frameworks, and polymers of intrinsic microporosity. Additionally, the adoption of biobased green solvents, such as Cyrene and γ-valerolactone, provides viable substitutes for hazardous dipolar aprotic solvents traditionally used in membrane fabrication. The incorporation of biopolymers, including cellulose derivatives and polyhydroxyalkanoates, further enhances the sustainability of polymeric membranes. To mitigate membrane waste, circular economy strategies, including downcycling, upcycling, and repreparation via covalent adaptable networks, offer promising pathways for extending membrane lifecycles and minimizing environmental impact.