A new crystalline lithium-ion conducting material, LiSnS with an ortho-composition, was prepared by a mechanochemical technique and subsequent heat treatment. Synchrotron X-ray powder diffraction was used to analyze the crystal structure, revealing a space group of P6/ mmc and cell parameters of a = 4.01254(4) Å and c = 6.39076(8) Å. Analysis of a heat-treated hexagonal LiSnS sample revealed that both lithium and tin occupied either of two adjacent tetrahedral sites, resulting in fractional occupation of the tetrahedral site (Li, 0.375; Sn, 0.125). The heat-treated hexagonal LiSnS had an ionic conductivity of 1.1 × 10 S cm at room temperature and a conduction activation energy of 32 kJ mol. Moreover, the heat-treated LiSnS exhibited a higher chemical stability in air than the LiPS glass-ceramic.