Soil water status plays an important role in growth-yield and grape quality of Vitis vinifera (L.). In some cases, periods of moderate water stress have been indicated to exert a positive effect on the quality of grape production. However, prolonged water stress may have a strong negative affect grapevine photosynthesis and grape yield, especially in dry Mediterranean environments. Biochar is a co-product of a thermochemical conversion of biomass that is recognized to be a beneficial soil amendment, which when incorporated into the soil increases soil water retention. We investigated the effect of two rates of biochar application (22 and 44 ton ha−1) on plant water relations of V. vinifera in a field experiment in central Italy. Biochar obtained from the carbonization of orchard pruning waste was applied to the soil over two consecutive growing seasons. The treatments did not show a significant increase in soil hydrophobicity. Moreover, soil analysis and ecophysiological measurements indicated a substantial relative increases in available soil water content compared to control soils (from 3.2% to 45% in the 22 and 44 ton ha−1 application rates, respectively) and in leaf water potential (24–37%) during droughts.