Energy-storage systems are considered as a key technology for energy and mobility transition. Because traditional batteries have many drawbacks, there are tremendous efforts to develop so-called postlithium systems. The magnesium-sulfur (MgS) battery emerges as one alternative. Previous studies of Mg-S batteries have addressed the environmental footprint of its production. However, the potential impacts of the use-phase are not considered yet, due to its premature stage of development. Herein, a first prospective look at the potential environmental performance of a theoretical Mg-S battery for different use-phase applications is given to fill this gap. By means of the life cycle assessment (LCA) methodology, an analysis of different scenarios and a comparison with other well-established technologies are conducted. The results suggest that the environmental footprint of the Mg-S is comparable with that of the commercially available counterparts and potentially outperforms them in several impact categories. However, this can only be achieved if a series of technical challenges are first overcome.