Objective: Patients suffering from major depressive disorder (MDD) experience impaired functioning and reduced quality of life, including an elevated risk of episode return. MDD is associated with high societal burden due to increased healthcare utilization, productivity losses, and suicide-related costs, making the long-term management of this illness a priority. The purpose of this study is to evaluate the cost-effectiveness of mindfulness-based cognitive therapy (MBCT), a first-line preventative psychological treatment, compared to maintenance antidepressant medication (ADM), the current standard of care. Method: A cost–utility analysis was conducted over a 24-month time horizon to model differences between MBCT and ADM in cost and quality-adjusted life years (QALY). The analysis was conducted using a decision tree analytic model. Intervention efficacy, utility, and costing data estimates were derived from published sources and expert consultation. Results: MBCT was found to be cost-effective compared to maintenance ADM over a 24-month time horizon. Antidepressant pharmacotherapy resulted in 1.10 QALY and $17,255.37 per patient on average, whereas MBCT resulted in 1.18 QALY and $15,030.70 per patient on average. This resulted in a cost difference of $2,224.67 and a QALY difference of 0.08, in favor of MBCT. Multiple sensitivity analyses supported these findings. Conclusions: From both a societal and health system perspective, utilizing MBCT as a first-line relapse prevention treatment is potentially cost-effective in a Canadian setting. Future economic evaluations should consider combined treatment (e.g., ADM and psychotherapy) as a comparator and longer time horizons as the literature advances.