To enhance Li+ transport in all‐solid‐state batteries (ASSBs), harnessing localized nanoscale disorder can be instrumental, especially in sulfide‐based solid electrolytes (SEs). In this investigation, the transformation of the model SE, Li3PS4, is delved into via the introduction of LiBr. 31P nuclear magnetic resonance (NMR)unveils the emergence of a glassy PS43− network interspersed with Br−. 6Li NMR corroborates swift Li+ migration between PS43− and Br−, with increased Li+ mobility indicated by NMR relaxation measurements. A more than fourfold enhancement in ionic conductivity is observed upon LiBr incorporation into Li3PS4. Moreover, a notable decrease in activation energy underscores the pivotal role of Br− incorporation within the anionic lattice, effectively reducing the energy barrier for ion conduction and transitioning Li+ transport dimensionality from 2D to 3D. The compatibility of Li3PS4 with Li metal is improved through LiBr incorporation, alongside an increase in critical current density from 0.34 to 0.50 mA cm−2, while preserving the electrochemical stability window. ASSBs with 3Li3PS4:LiBr as the SE  showcase robust high‐rate and long‐term cycling performance. These findings collectively indicate the potential of lithium halide incorporation as a promising avenue to enhance the ionic conductivity and stability of SEs. Incorporation of Br‐ into the β‐Li3PS4 anion sublattice creates local disorder and diversifies coordinating partners of Li+, yielding fast‐ion transport with lowered activation energy barriers and improved compatibility with Li metal anodes. This approach holds promise for enhancing the ion conduction and stability of sulfide‐based solid electrolytes for all‐solid‐state batteries.