Olive leaves, an abundant agro-industrial by-product, represent a valuable source of phenolic compounds. Cultivars grown in Brazil remain underexplored at the metabolomic level, particularly regarding strategies for their valorization. Extraction methods, such as ultrasound-assisted extraction and infusion, offer distinct pathways for utilizing this by-product. This study aimed to characterize the phenolic metabolome (UHPLC-DAD-MS/MS) and antioxidant activity (ABTS and DPPH assays) of olive leaves from two cultivars grown in Brazil (Coratina and Picual), comparing ultrasound-assisted extracts and infusion. Multivariate analyses (principal component analysis and hierarchical clustering) were applied to evaluate sample discrimination and correlations between phenols and antioxidant activity (Spearman). The phenolic profile was complex, dominated by secoiridoids and including flavonoids, and was more efficiently recovered by ultrasound-assisted extraction. A clear distinction was observed between extraction methods and cultivars, with differences mainly attributed to the relative abundance of medium- and low-abundance metabolites. Correlation analysis indicated positive associations between multiple phenolic compounds and antioxidant activity, suggesting a synergistic effect driven by the overall metabolic profile. These findings provide novel metabolomic insights into olive leaves from Brazilian-grown cultivars and demonstrate that extraction strategy plays a key role in their valorization. Ultrasound-assisted extraction maximizes compound recovery, whereas infusions represent an accessible home-based method for enhancing antioxidant intake.