Abstract: Purpose: Combat deployment increases exposure to potentially traumatic events. Perceived social support (PSS) may promote health and recovery from combat trauma. This systematic review and meta-analysis aimed to synthesize studies investigating the level of PSS and associated factors among (ex-)military personnel who served in the Iraq/Afghanistan conflicts. Methods: Five electronic databases were searched in August 2023 and searches were restricted to the beginning of the Iraq/Afghanistan conflicts in 2001. The search was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A quality assessment was carried out, and a meta-analysis and narrative synthesis were performed. Results: In total, 35 papers consisting of 19,073 participants were included. Of these, 31 studies were conducted in the United States (US) and 23 were cross-sectional. The pooled mean PSS score was 54.40 (95% CI: 51.78 to 57.01). Samples with probable post-traumatic stress disorder had a lower mean PSS score (44.40, 95% CI: 39.10 to 49.70). Approximately half of the included studies (n = 19) investigated mental health in relation to PSS, whilst only four explored physical health. The most frequently reported risk factors for low PSS included post-traumatic stress disorder, depression and anxiety, whilst post-traumatic growth and unit support were protective factors. Conclusion: Higher levels of PSS were generally associated with more positive psychosocial and mental health-related outcomes following deployment. PSS should be targeted in psychosocial interventions and education programmes. Future research should investigate PSS in (ex-)military personnel across other countries and cultures, based on the lack of studies that focused on PSS in countries outside of the US.