The effects of Bacillus sp. SLS18, a plant-growth-promoting endophyte, on the biomass production and Mn/Cd uptake of sweet sorghum (Sorghum bicolor L.), Phytolacca acinosa Roxb., and Solanum nigrum L. were investigated. SLS18 displayed multiple heavy metals and antibiotics resistances. The strain also exhibited the capacity of producing indole-3-acetic acid, siderophores, and 1-aminocyclopropane-1-carboxylic acid deaminase. In pot experiments, SLS18 could not only infect plants effectively but also significantly increase the biomass of the three tested plants in the presence of Mn/Cd. The promoting effect order of SLS18 on the biomass of the tested plants was sweet sorghum > P. acinosa > S. nigrum L. In the presence of Mn (2,000 mg kg(-1)) and Cd (50 mg kg(-1)) in vermiculite, the total Mn/Cd uptakes in the aerial parts of sweet sorghum, P. acinosa, and S. nigrum L. were increased by 65.2%/40.0%, 55.2%/31.1%, and 18.6%/25.6%, respectively, compared to the uninoculated controls. This demonstrates that the symbiont of SLS18 and sweet sorghum has the potential of improving sweet sorghum biomass production and its total metal uptake on heavy metal-polluted marginal land. It offers the potential that heavy metal-polluted marginal land could be utilized in planting sweet sorghum as biofuel feedstock for ethanol production, which not only gives a promising phytoremediation strategy but also eases the competition for limited fertile farmland between energy crops and food crops.