Glacier retreat in cold regions exposes new terrain for plant colonization. However, the roles of soil microbiomes in plant establishment and performance on newly-exposed forefields have rarely been assessed. Here, we compared the survival of Antarctic pearlwort (Colobanthus quitensis) individuals grown for three years in sterilised and unsterilised soils at sites initially at 30 m, 100 m and 300 m from three retreating Maritime Antarctic glaciers. We also installed open top chambers (OTCs), which increased air temperatures by ∼1.8 °C and reduced soil water potential by ≤ 4 kPa, on one forefield to test the effects of warming on C. quitensis survival and the soil microbiome. The main driver of plant performance was distance from glacier fronts, with a 32 kPa reduction in soil water potential apparently explaining reduced plant survival at 300m compared with 30 m from glaciers. Soil sterilisation had few effects on plant survival at 30 m and 100 m, but reduced survival at 300 m, which was attributable to reductions in beneficial plant-microbial interactions. Effects of OTCs on plant survival were amplified with distance from glacier and sterilisation, with plants not surviving in chambered and sterilised soil at 300 m after three years. Soil bacterial functionality altered from a phototrophic community at 30 m to a more specialized chemoheterotrophic community at 100–300 m. Fungal ortholog groups showed transfer RNA and ribosome biogenesis to be enriched in soil at 30 m, with spliceosomes and messenger RNA synthesis being more frequent at 300 m. We propose that soil microbiomes improve the environmental tolerance of C. quitensis through enhanced physiological performance, which in turn improves survival and facilitates the species’ colonization of newly-exposed glacier forefield soils. These plant-microbe interactions are likely to become increasingly important as the climate of Maritime Antarctica changes over future decades.