Soil composition plays a critical role in viticulture, influencing grapevine physiology and modulating wine characteristics through edaphic-climatic interactions. In the semiarid S & atilde;o Francisco Valley of Brazil, where viticulture is expanding under tropical conditions, the effects of soil variability on wine quality remain underexplored. This study assessed the impact of five distinct Ultisol types, differing in texture, drainage capacity, and mineralogy, on the phenolic profile and antioxidant capacity of Syrah and Tempranillo red wines. Grapes were cultivated under uniform vineyard management practices, and microvinification followed standardized protocols. Wine samples were analyzed for physicochemical attributes, total phenolics, flavonoid subclasses, and antioxidant activity. Ultisols with higher clay content and better water retention promoted the accumulation of anthocyanins and stilbenes, enhancing antioxidant potential. Syrah was more responsive to edaphic variability than Tempranillo, particularly under soils with higher water-holding capacity. Despite these soil-driven effects, interannual variation in wine composition was predominantly governed by climatic factors, notably temperature and precipitation. Principal component analysis revealed that both soil type and vintage shaped distinct enological profiles, highlighting the synergistic influence of pedological and climatic elements on grape and wine chemistry. These findings emphasize the need for soil-informed vineyard management strategies to optimize phenolic expression and antioxidant capacity in tropical terroirs. This study contributes to a deeper understanding of soil-plant-wine interactions in semiarid viticulture and reinforces the role of soil variability as a determinant of enological potential in emerging wine regions.