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Background Electroconvulsive therapy (ECT) is among the most effective treatments for treatment-resistant mood disorders.Objective This study aims to meta-analyse the effects of ECT on all-cause mortality and suicide deaths in severe unipolar or bipolar depression using longitudinal studies.Study selection and analysis PubMed/MEDLINE, PsycINFO, Cochrane Library, Embase and Google Scholar were searched from inception through 21 January 2025. Inclusion criteria were: (1) patients with diagnoses of mental disorders; (2) intervention consisted of ECT compared with placebo, usual care or another intervention; (3) all-cause mortality and suicide deaths as outcomes measures; and (4) clinical trial or longitudinal cohort study designs where the aforementioned interventions preceded the observations of outcome measures. Adjusted HR with their corresponding 95% CIs were estimated using random-effects models. Moderator analyses were also performed.Findings Overall, 17 studies consisting of 1 182 501 individuals (n=40 867 for patients with ECT, n=1 141 634 for patients with non-ECT) were included. 94.1% of the studies focused on patients with unipolar or bipolar depression and one study was focused on schizoaffective disorder. ECT was associated with a reduction in risk of all-cause mortality (HR 0.70 (95% CI 0.61 to 0.81); p<0.001), a finding that was consistent at 3 months, 6 months and 12 months of follow-up. Regions had a moderating effect; Japan had the largest effect size (HR 0.17 (95% CI 0.04 to 0.72)) and Denmark had the smallest (HR 0.87 (95% CI 0.83 to 0.92)). ECT was associated with a reduction in suicide risk at 3 months of follow-up (HR 0.53 (95% CI 0.39 to 0.72); p<0.001) but not at 1, 6 or 12 months of follow-up.Conclusions ECT is associated with a reduced risk of all-cause mortality. However, ECT use for suicide protection appears transient and inconsistent.Clinical implications ECT may be safely used among patients with severe unipolar or bipolar depression.PROSPERO registration number CRD42025641749.