The xNa2S·(100 − x)P2S5 (mol%; x = 67, 70, 75 and 80) glasses were prepared by mechanochemical processing. Composition dependence of local structure, thermal behavior and electrical conductivity of the prepared glasses were examined. NMR and Raman spectroscopic studies revealed that the xNa2S·(100 − x)P2S5 glasses were composed of the thiophosphate units corresponding to their nominal compositions. The room temperature conductivities of the glasses increased with an increase in the Na2S content and attained a maximum at the x = 80 composition; the highest conductivity is 1 × 10−5 S cm−1. The xNa2S·(100 − x)P2S5 glass–ceramics were obtained by heating the glasses beyond their crystallization temperatures. The relationship between conductivity and crystalline phase was studied for the glass–ceramics. The glass–ceramics at the compositions of x = 70 and 75 exhibited higher conductivities than those of corresponding glasses due to the precipitation of the superionic cubic Na3PS4 crystal. In particular, the x = 75 glass–ceramic showed the highest conductivity of 2 × 10−4 S cm−1 at 25 °C and the lowest activation energy of 27 kJ mol−1. In addition, the x = 75 glass–ceramic was electrochemically stable against sodium deposition and dissolution. The 75Na2S·25P2S5 glass–ceramic electrolyte with high conductivity and high electrochemical stability is suitable for all-solid-state sodium rechargeable batteries.