The prevalence of anxiety and depression has increased globally, necessitating effective therapeutic interventions. Mindfulness-based therapy (MBT) has emerged as a promising approach in clinical psychology to address these mental health issues. This study aimed to evaluate the efficacy of MBT in reducing symptoms of anxiety and depression among adults. A randomized controlled trial was conducted with participants recruited from mental health clinics in Estonia, Greece, and South Korea. Participants were assigned to either the MBT group or a control group receiving standard cognitive-behavioral therapy (CBT). Psychological assessments were conducted at baseline, post-treatment, and at a 6-month follow-up. The primary outcome measures included the Beck Anxiety Inventory and the Beck Depression Inventory. Findings indicated that participants in the MBT group exhibited significant reductions in anxiety and depression scores compared to the control group, both immediately post-treatment and at follow-up. The results suggest that MBT may offer a viable alternative or complement to traditional CBT for managing anxiety and depression. Further research should explore the long-term benefits and potential mechanisms underlying mindfulness interventions. This study contributes to the growing body of evidence supporting the integration of mindfulness practices in clinical psychology settings.