The projected increase in mean temperatures caused by climate change is expected to have detrimental impacts on berry quality. Microorganisms as arbuscular mycorrhizal fungi (AMF) produce numerous benefits to host plants and can help plants to cope with abiotic stresses such as high temperature. The aims of this research were to characterise the response of three clones of Vitis vinifera L. cv. Tempranillo to elevated temperatures and to determine whether AMF inoculation can improve berry antioxidant properties under these conditions. The study was carried out on three fruit-bearing cuttings clones of cv. Tempranillo (CL-260, CL-1048 and CL-1089) inoculated with AMF or uninoculated and subjected to two temperature regimes (day–night: 24°C−14°C and 28°C−18°C) during berry ripening. Results showed that clonal diversity of Tempranillo resulted in different abilities to respond to elevated temperature and AMF inoculation. In CL-1048, AMF inoculation improved parameters related to phenolic maturity such as anthocyanin content and increased antioxidant activity under elevated temperature, demonstrating a protective role of AMF inoculation against warming effects on berry quality. The results therefore suggest that selection of new clones and/or the implementation of measures to promote the association of grapevines with AMF could be strategies to improve berry antioxidant properties under future warming conditions.