Agricultural irrigation management is considered more necessary than ever, as climate change directly threatens natural resources and the growth of economically important Mediterranean crops such as grapevines. In this work, the metabolic characteristics of grapevine plants were assessed under rational (100% of AW) and irrigation-deficit (57% of AW) conditions, with the application of a Sinorhizobium meliloti biostimulant. The study was carried out at the greenhouse of the Department of Agriculture of the University of Ioannina in 9 L pots connected with a drip irrigation system, where four treatments were established: Treatment B (100% of AW and S. meliloti application), treatment SB (57% of AW and S. meliloti application), C (100% of AW), and SC (57% of AW). During the experiment that lasted 5 months, the grapevine leaf area (cm²) was measured, and proline (µmol g⁻¹ Fresh Leaf), total phenolic (mg GAE g⁻¹ Dry Leaf), and chlorophyll (µg cm⁻²) content were assessed as indicators of abiotic stress. The data of the experiment showed that the use of S. meliloti could act as a biotic stress inhibitor due to the irrigation deficit caused in the grapevine cultivation. This case study complements the literature on the grapevine cultivation management practices in the scenario of imposing irrigation regimes due to climate change.