OBJECTIVES: To investigate the effects of the Mindfulness-Based Health Promotion (MBHP) program on quality of life (QOL) and well-being in older adults compared to an active control group. METHOD: A randomized controlled trial nested within a cohort study was conducted. Participants were allocated to either the MBHP intervention or an active control group (ACG) receiving computer-based cognitive stimulation. Outcomes included QOL, psychological health, sleep quality, and religiosity. Both interventions lasted four months. A mixed-methods approach was used, collecting qualitative and quantitative data at baseline and post-intervention. RESULTS: Statistically significant improvements in QOL were observed only in the ACG. However, the MBHP group showed improvements in stress, anxiety, intrinsic religiosity, and sleep quality compared to the ACG. Qualitative findings indicated enhanced perceptions of social support, self-awareness, self-care, and sleep quality in the MBHP group. Notably, a discrepancy emerged between the QOL quantitative results and the subjective improvements described in interviews. CONCLUSION: The MBHP program did not significantly improve QOL compared to the cognitive stimulation control. Nonetheless, well-being indicators were positively impacted in the MBHP group. Future research should explore which profiles of older adults might benefit most from regular mindfulness practice.