Steering plant and soil microbiomes is increasingly viewed as a key strategy to reduce agriculture’s dependence on synthetic pesticides. Yet, this approach remains challenging due to the extraordinary diversity of microbial taxa and functions. Which ones should be promoted to improve crop protection, and how can this protection be sustained over time? We address these questions using grapevine (Vitis vinifera) as a model system. Our goal is to harness the grapevine microbiome to enhance protection against downy mildew (Plasmopara viticola), a major disease responsible for severe yield losses and extensive fungicide use. We combined epidemiological data with microbiome composition profiles to identify microbial taxa consistently associated with reduced disease incidence and severity. We also compared the microbiomes of susceptible European cultivars with those of naturally resistant American species (Vitis labrusca, V. aestivalis). These insights guided the design of Synthetic Microbial Communities (SynComs) composed of bacteria, yeasts, and filamentous fungi previously isolated from low-disease vineyards through a culturomic approach using a novel grape leaf extract–based medium. In vitro confrontation assays revealed that these SynComs exerted biocontrol activity against P. viticola, largely mediated by their fungal component. Ongoing metabolomic and transcriptomic analyses aim to unravel the mechanisms underlying this microbiome-mediated protection. Together, these results open new avenues for microbiome-based biocontrol through (i) targeted inoculation of protective consortia and (ii) agroecological practices that naturally enhance beneficial microorganisms.