Magnesium-sulfur (Mg-S) batteries are a promising energy storage system; however, the short cycle life, low coulombic efficiency, and the shuttle effect of polysulfide hinder its practical use. Electrolyte additives are a powerful method to optimize the electrochemical performance of Mg-S electrolytes. Ammonium bromide (NH4Br) is used as an inorganic electrolyte additive in the halogen-free electrolyte (HFE) to guide homogeneous Mg deposition. It can be observed that the addition of NH4Br decreases the activation energy values from 0.14 eV to 0.10 eV and decreases the value of Mg2+ stripping/plating overpotential. It is found that the introduction of NH4Br to HFE enhances the cycle life and the initial discharge capacity (∼1662 mAhg−1) of the Mg-S cells compared with the cells using free NH4Br that fade fast and deliver low initial discharge capacity of ∼ 184 mAh g−1. A BaTiO3 (BTO) has been utilized as a modified separator to overcome the polysulfide dissolution issue in the cell. The surface of the cell's anode applying a modified separator shows half wt% S content compared with the bare cell after cycling. This study opens further research for developing novel electrolyte schemes for magnesium-sulfur battery applications.