Abstract: Perinatal mental health disorders affect 1 in 5 mothers, with military life introducing unique stressors that may exacerbate these conditions. Non-serving military spouse mothers may be particularly vulnerable, yet their specific needs remain underexplored. Understanding factors affecting their mental health is crucial, given its impact on both individual wellbeing and military personnel retention in the U.K. This review systematically examines the factors influencing perinatal mental health in non-serving military spouse mothers, identifying key stressors and research gaps. A comprehensive search of eight electronic databases—ProQuest, MEDLINE, PsycINFO, PsycArticles, CINAHL, EMBASE, and Web of Science—was conducted in April 2024, with relevant data extracted. Due to heterogeneity among studies, a textual narrative synthesis was applied. Seven U.S-based studies met inclusion criteria, though all were of limited quality. No studies focused on European non-serving military mothers. Deployment emerged as a primary stressor, with perceived risk and timing of deployments in relation to pregnancy affecting mental health outcomes. However, broader perinatal experiences were largely unexamined. Findings suggest military-specific factors, particularly spousal deployment, influence non-serving spouse mothers’ perinatal mental health. However, existing research is low quality, overly focused on deployment, U.S-centric, and limited in scope within the perinatal period. Future research should explore the U.K Armed Forces context, consider factors beyond deployment, and encompass the entire perinatal period. These insights are essential for healthcare professionals and policymakers to develop targeted interventions and military-informed perinatal care.