Salt stress is recognized as a significant factor influencing crop growth and yield. The ability of Bacillus megatherium to promote plant growth and enhance stress resistance has been extensively documented. The effect of Bacillus megatherium on sorghum seed germination and seedling growth under salt stress was investigated in this study. The biochemical mechanisms for improving salt tolerance in sorghum were explored. The results indicate that at NaCl concentrations of 0 and 200 mmol/L, the germination rate of sorghum seeds increased by 7.78% and 17.78%, respectively, compared to the non-inoculated control. Enhanced growth, as measured by plant height, stem thickness, and biomass, was observed in inoculated sorghum seedlings in comparison to their uninoculated counterparts. Furthermore, chlorophyll content in sorghum leaves increased by 23.57%, photosynthetic efficiency improved, the synthesis of aboveground biomass was enhanced, soluble protein levels rose by 35.81%, and malondialdehyde levels decreased by 45.68%. These improvements are believed to contribute to the enhanced tolerance of sorghum seedlings to salt stress. The findings of this study provide new insights into the development and application of biological fertilizers for managing saline-alkali soils, which holds significant practical implications.