The aim of this study was to investigate the effect of chia supplementation (Salvia hispanica L.) on blood pressure (BP) and its associated cardiometabolic factors in treated and untreated hypertensive individuals. The subjects were randomly assigned to one of the following groups: the hypertensive-drug treated (CHIA-MD, n = 10), hypertensive untreated (CHIA-NM, n = 9) and placebo (PLA-MD, n = 7) groups. The subjects consumed 35 g/day of either chia flour or a placebo for 12 weeks. The clinical and ambulatory BP, inflammation, oxidative stress and markers for nitric oxide were measured. While the PLA-MD group showed no changes in BP, there was a reduction in the mean clinical blood pressure (MBP) in the CHIA (111.5 ± 1.9 to 102.7 ± 1.5 mmHg, p < 0.001) and CHIA-MD (111.3 ± 2.2 to 100.1 ± 1.8 mmHg, p < 0.001) groups. The CHIA-NM group showed no reduction in the MBP but did show a decreased systolic BP (146.8 ± 3.8 to 137.3 ± 3.1 mmHg, p < 0.05). The clinical BP reduction was demonstrated by a 24 h ambulatory systolic reduction in all of the supplemented groups. However, the mean ambulatory BP was reduced only in the CHIA (98.1 ± 2.4 to 92.8 ± 2.2 mmHg, p < 0.05) group, and there was no change in the diastolic component in either of the CHIA groups. The lipid peroxidation was reduced in the CHIA (p = 0.04) and CHIA-NM (p = 0.02) groups compared with the PLA-MD group. A reduction in the plasma nitrite levels was observed only in the CHIA group (p = 0.02). Chia flour has the ability to reduce ambulatory and clinical BP in both treated and untreated hypertensive individuals.