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Objective We synthesised the literature to establish the prevalence of post-traumatic stress disorder (PTSD) among current and former members of the Canadian Armed Forces (CAF).Methods We searched EMBASE, MEDLINE, PsycINFO and CINAHL from inception until June 2024 for studies reporting the prevalence of PTSD among Canadian military personnel and veterans. We performed a Freeman-Tukey double arcsine transformation to stabilise the variance, then pooled the prevalence of PTSD across studies using a random-effects model. We used the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach to assess the certainty of evidence and the Instrument to Assess the Credibility of Effect Modification Analyses (ICEMAN) to assess the credibility of subgroup effects. We followed the Meta-analysis of Observational Studies in Epidemiology (MOOSE) and Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines to report our findings.Results We included 31 studies without overlapping datasets (68 364 participants). The pooled prevalence of PTSD was 37.1% (95% CI 29.0% to 45.7%); however, we found evidence of credible subgroup effects based on representativeness of the study population and veteran status. High certainty evidence from eight studies (n=46 382) shows the prevalence of PTSD among active-duty CAF members is 4.9% (95% CI 3.6% to 6.4%). Moderate certainty evidence from six studies (n=15 626) suggests the prevalence of PTSD among CAF veterans is probably 12.2% (95% CI 7.3% to 18.2%).Conclusions We found high certainty evidence that 5 in every 100 active-duty CAF members live with PTSD and moderate certainty evidence that 12 in every 100 Canadian veterans probably live with PTSD. Our findings highlight the need for PTSD screening and access to evidence-based care for current and former CAF members.