BACKGROUND: Music can directly influence emotions, the regulation of which are known to be impaired in major depressive disorder (MDD). While music therapy (MT) could be an effective complement to treat MDD, studies investigating such effects have not yet yielded conclusive results. We hypothesized that group music therapy (GMT) might lead to a significant reduction of depressive symptoms (DS). METHODS: In a randomized controlled trial, 102 women with current MDD were randomly assigned to an intervention group receiving GMT or a waitlist control group. Data assessment was conducted pre- (T0), post- (T1), and at a 10-week follow-up to (T2) the intervention. DS as the primary outcome were assessed via observer-rated (Hamilton Depression Rating Scale, T0-T1), self-rated (Beck Depression Inventory, T0-T1-T2), and ecological momentary (T0-T1) assessments. Secondary effects on emotion and mood regulation strategies, and quality of life (QoL), were measured T0-T1-T2. RESULTS: The results suggest non-significant effects of the GMT on a descriptive level on self-reported and observer rated DS and statistically significant effects on DS in everyday life, QoL, and regulation strategies, with larger effects from T0-T1 than from T0-T1-T2. LIMITATIONS: The generalizability is limited by the high dropout rate and data loss due to the COVID-19 pandemic, the fact that long-term effects of GMT are not assured, and the homogeneous gender (female) of the sample. CONCLUSIONS: GMT is an economical approach to treat MDD, yielding health-promoting effects regarding DS, emotion regulation, and QoL. Manualization and further evaluation of MT is strongly recommended.