Background/Objective: Hypertension is a leading preventable cause of cardiovascular disease, affecting over one billion people worldwide. Berry-derived bioactive compounds may influence vascular function and blood pressure. This systematic review and meta-analysis evaluated the effects of oral berry supplementation on blood pressure in adults with elevated blood pressure or hypertension and additionally assessed its effects on related cardiometabolic outcomes. Methods: PubMed, CENTRAL, Embase, and Scopus were searched from inception to May 2025. Eligible studies were randomized controlled trials (RCTs) enrolling adults with hypertension or elevated blood pressure who received oral berry supplementation compared with placebo, standard diet without berries or usual care. Design-specific analytical strategies were employed to preserve within-participant comparisons in cross-over trials. Random-effects meta-analyses were conducted using the restricted maximum likelihood estimator, and the certainty of evidence was assessed using the GRADE framework. PROSPERO registration: CRD420251046489. Results: Nine RCTs (547 participants) were included. Berry supplementation did not significantly reduce resting systolic (MD −2.35 mmHg; 95% CI −4.98 to 0.29; I² = 65%) or diastolic blood pressure (MD −1.04 mmHg; 95% CI −2.38 to 0.76; I² = 60%). A significant reduction in 24 h ambulatory diastolic blood pressure was observed (MD −1.11 mmHg; 95% CI −2.04 to −0.17; I² = 0%), driven by cross-over trials. No significant effects were found for vascular, lipid, or inflammatory markers. Certainty of evidence was low to very low across all outcomes. Conclusions: Current evidence does not support a consistent effect of berry supplementation on blood pressure or related cardiometabolic outcomes in this population, given the low to very low certainty of the available evidence.