Background <p>High depression rates persist despite the availability of gold-standard psychological treatments. There is growing research evidence for schema therapy’s effectiveness for depression. However, the adoption of schema therapy in clinical practice has outstripped the pace of research. The most recent model of schema therapy (the mode model) is increasingly being used over the basic model because of its experiential techniques and expansion beyond early maladaptive schemas. This systematic review aimed to explore the impact of schema therapy and its treatment models (basic and mode) on symptom reduction in depressive disorders.</p> Method <p>A systematic literature search was conducted in PsycINFO, MEDLINE, Embase, Scopus, and the Cochrane Library on 23 November 2023 and updated on 1 June 2024. Studies were excluded if they used combined therapies, child samples, or lacked a formal depression diagnosis, depressive outcome data, or an English translation. The review was conducted following PRISMA guidelines and study quality was evaluated using the Joanna Briggs Institute Critical Appraisal Checklists.</p> Results <p>Seven studies (<i>N</i> = 580) with a range of methodological designs, outcomes measures, and diagnoses were identified. All studies found that schema therapy had a significantly positive impact on depressive outcomes and large effect sizes pre-post treatment were observed. The studies suggest that schema therapy was non-inferior to established treatments such as CBT and had similar efficacy to short-term psychoanalytic supportive psychotherapy and individual supportive therapy. Included studies also indicated that the dosage of sessions may be important in ensuring significantly large treatment effects.</p> Conclusions <p>The literature indicates that schema therapy is effective for reducing depressive symptoms in depressive disorders. The strength of the findings are limited by the modest number of studies and sample sizes therein. However, current evidence lends more support to the mode model’s effectiveness in depressive symptom reduction. Higher schema therapy dosage may elicit pronounced treatment benefits for depressive disorders, even with chronic and comorbid psychopathologies. Comparative RCTs of the different schema therapy models and between schema therapy and CBT are required to advance the evidence base.</p> Systematic review registration <p>PROSPERO (CRD42023480067).</p>