Despite increasing metals and metalloids (MM) human-driven soil contamination, how it simultaneously alters biodiversity and ecosystem functioning remains unknown. We used a wide gradient of a 170-year-old MM soil multi-contamination in Mediterranean scrublands to assess the effects of soil multi-contamination on multiple plant biodiversity facets, microbial communities and ecosystem multifunctionality (EMF). We found an overall positive effect of plant biodiversity on EMF mediated by microbial communities, and allowing to offset the negative impacts of MM soil multi-contamination, especially on soil water holding capacity and nitrogen content. The diversity of distant plant lineages was the key facet promoting EMF by enhancing microbial communities, whereas the subordinate species richness altered EMF. By developing a holistic approach of these complex relationships between soil multicontamination, plant biodiversity, microbial communities and ecosystem functioning, our results reveal the potential of plant biodiversity, and especially the diversity of evolutionary distant species, to offset the alteration of ecosystem functioning by MM soil multicontamination. In this worldwide decade of ecosystems restoration, our study helps to identify relevant facets of plant biodiversity promoting contaminated ecosystem functioning, which is crucial to guide and optimize management efforts aiming to restore ecosystems and preserve human health.