Background <p>Suicide is a major public health problem in South Korea, where the suicide rate substantially exceeds the OECD average. However, research investigating the moderating role of social vulnerability on the relationship between mental health outcomes and suicide risk is limited. The present study aims to investigate (i) whether socially vulnerable groups (SVGs) exhibit worse mental health, (ii) whether social vulnerability independently predicts suicide risk, and (iii) whether social vulnerability moderates the associations between psychosocial factors and suicide risk.</p> Methods <p>From October 6 to October 12, 2023, an online survey was conducted with 1,000 Seoul residents stratified by sex, age, and residential district. After excluding invalid responses, 995 participants were analyzed. In this study, we examined group differences using independent samples t-tests, predictors of suicide risk via multivariate regression with heteroscedasticity-consistent standard errors (HC3), and conducted moderation analyses using PROCESS Macro Model 1.</p> Results <p>238 out of 995 respondents were classified as SVG (23.9%). SVGs exhibited worse mental health outcomes and a higher risk of suicide compared to non-SVGs. Social vulnerability remained a significant independent predictor of suicide risk after controlling for psychosocial covariates. Moderation analyses revealed that social vulnerability significantly amplified the associations between depression and suicide risk (B = 0.12, <i>p</i> = .008) and between PTSD symptoms and suicide risk (B = 0.19, <i>p</i> &lt; .001).</p> Conclusion <p>SVGs were more vulnerable to suicide risk when they were exposed to psychosocial risk factors, particularly in terms of depression and post-traumatic distress. Together, our findings highlight social vulnerability as a critical factor in suicide prevention strategies. This study supports the importance of targeted suicide prevention and early mental health intervention for SVGs.</p>