Increasing evidence suggests that invasive plants can sustain high growth rates in heavy metal-enriched environments, while native species do not contribute to their invasion success. However, the underlying mechanisms are poorly understood. This study examined the invasive plant Phytolacca americana and native Phytolacca acinosa in Cd-contaminated soils in China. The results showed that, while native plant biomass decreased at higher soil Cd concentrations, invasive plant biomass remained unaffected. Soil enzyme activities decreased with increasing Cd concentration but were higher in soils where invasive plants grew than those in soils where native plants grew. Phytolacca americana accumulated more Cd, particularly in the leaves and under higher soil Cd concentrations. Native seed germination was inhibited with increasing litter-Cd concentration, whereas invasive seed germination was unaffected. These findings suggest that the ability of the invasive species to mitigate the negative effects of Cd pollution on soil enzyme activities contributed to their higher Cd-tolerance by maintaining soil nutrient availability. Additionally, higher leaf-Cd levels in invasive plants constitute an elemental defence. Overall, heavy metal pollution not only favoured invasive plants by suppressing native plant growth but may have also promoted invasion through the effects of Cd accumulation in invasive litter on native seed germination.