Abstract: Introduction: Repetitive transcranial magnetic stimulation (rTMS) is an effective, non-invasive treatment option for treatment-resistant posttraumatic stress disorder (TR PTSD) and treatment-resistant depression (TRD). This study assesses left-sided high-frequency (LSHF) rTMS on symptoms of Canadian Armed Forces (CAF) and Royal Canadian Mounted Police (RCMP) members with TRD and TR PTSD at the Carewest Operational Stress Injury clinic. Methods: This feasibility study used a quantitative longitudinal design. The study population included 28 CAF and RCMP members with TR PTSD and TRD, defined as lack of response to two antidepressants and one evidence-based psychotherapy. Patients concurrently undertook biological and psychological treatment as usual. Up to 30 sessions of LSHF rTMS were provided; non-responders switched to right-sided low-frequency (RSLF) rTMS after 20 sessions. Depression and PTSD symptoms were quantified using the PTSD Checklist for DSM-5 (PCL-5) and Patient Health Questionnaire-9 (PHQ-9) before treatment, every 10th session, and at completion. Outcomes were analyzed with one-way repeated-measures analysis of variance. Results: PHQ-9 scores decreased (p < 0.001) during rTMS treatment, from moderately severe depression at baseline (mean = 18) to moderate depression at the 20th (mean = 11) and 30th (mean = 10) sessions. Similarly, PCL-5 scores significantly decreased (p < 0.001), reaching sub-clinical threshold (initial mean = 48, 20th session mean = 33, and 30th session, mean = 31). Discussion: These findings support the efficacy of rTMS for reducing symptoms of TRD and TR PTSD in this population. Larger studies with sham rTMS comparison, blinding, and randomization are needed.