The growing global demand for freshwater—particularly in arid and semi-arid regions—has underscored the necessity of adopting sustainable water supply solutions, making seawater desalination a strategic, economic, and technological option. A comprehensive review of emerging technologies reveals that significant advancements have been achieved in recent years in both membrane and thermal methods, including improved membrane selectivity and permeability, reduced energy consumption, optimization of reverse osmosis processes, and the development of hybrid and multi-stage systems. However, key challenges such as high energy consumption, dependence on fossil fuels, the generation and discharge of highly concentrated brine, and extensive chemical use continue to limit the sustainability of these systems. Integrating renewable energy sources—particularly photovoltaic, solar-thermal, and wind energy systems—offers significant potential to reduce the carbon footprint and enhance environmental performance, though operational issues such as cooling, scaling, dust accumulation, and equipment durability must be managed. Environmental impact assessments indicate that brine discharge remains the most critical ecological challenge, and the use of advanced modeling, modern diffusers, resource recovery strategies, and minimal-discharge technologies can help mitigate its negative effects. The development of advanced fouling-resistant membranes, hybrid energy systems, and optimized energy consumption strategies is considered essential for achieving a sustainable and practical future in seawater desalination.