The global demand for lithium (Li) is rapidly increasing due to its essential role in lithium-ion batteries (LIBs), which power electric vehicles, electronics, and large-scale renewable energy storage systems. Conventional extraction from ores and brines involves multiple steps, including clarification, filtration, concentration, and purification, which consume high energy, utilize chemicals, and have significant environmental impacts. Alternative sources, including municipal and industrial wastewater, geothermal brines, and spent battery leachates, are gaining attention as potential sources of lithium. Although these sources contain lower lithium concentrations, they provide important benefits by supplementing the supply and reducing environmental discharge. Recent technological advances have improved the feasibility of recovering lithium from these unconventional sources. This review focuses on membrane-based recovery technologies, including nanofiltration membranes, supported liquid membranes, ion-imprinted membranes, ion-sieve membranes, membrane distillation crystallization, selective electrodialysis, and capacitive deionization. Each method is analyzed for its separation mechanisms, performance, advantages, and limitations. Overall, while considerable progress has been made in selectivity, efficiency, and environmental compatibility, challenges remain in terms of scalability, cost, and integration into existing systems. Future developments will require hybrid approaches, digital optimization, and collaborative efforts to establish sustainable and commercially viable pathways for lithium recovery.