Solid state electrolytic properties of mixtures of Li(BH4)0.75I0.25 and amorphous 0.75Li2S·0.25P2S5 are reported in this study. The enhanced Li-ion conductivities for the Li(BH4)0.75I0.25 phase after addition of 0.75Li2S·0.25P2S5 were found to be within the range for practical solid-state electrochemical storage near room temperature. The highest ionic conductivities are found for the borohydride/sulfide system at 1:2 wt ratio with ∼10−3 S cm-1 at room temperature and an activation energy of 0.30(2) eV. Combined experimental analyses with powder X-ray diffraction and infrared spectroscopy suggest that the synthesized material still include both [PS4 3−] and [BH4 −] entities. Density functional theory (DFT) calculations provide more insights about the origin of the observed ionic behavior according to the induced structural modifications in the BH4–BH4 interactions. Finally, the electrolyte functionality and its compatibility toward an active material are successfully demonstrated by means of cyclic voltammetry (Au vs. Li+/Li) in a large voltage window (up to 5 V) and battery cycling tests with TiS2 electrode, respectively.