Objective: Patients with severe mental illness have a high risk of suicide and frequently living eliminated from mainstream society, but the effects of social support on suicide-related behaviors among this crowd is inconclusive. The present study aimed to explore such effects among patients with severe mental illness. Methods: We implemented a meta-analysis and a qualitative analysis of relevant studies published before February 6, 2023. Correlation coefficients (r) and 95 % CI were selected as the effect size index in meta-analysis. Studies that did not report correlation coefficients were employed for qualitative analysis. Results: Out of 4241 identified studies, 16 were identified in this review (6 for meta-analysis, 10 for qualitative analysis). The meta-analysis presented that the pooled correlation coefficients (r) were - 0.163 (95%CI = -0.243, -0.080, P < 0.001), suggesting a negative correlation between social support and suicidal ideation. The subgroup analysis showed that this effect works in all bipolar disorder, major depression, and schizophrenia. Concerning qualitative analysis, social support presented positive effects on reducing suicidal ideation, suicide attempts, and suicide death. The effects were consistently reported in female patients. However, there existed some unaffected results in males. Limitations: The included studies were from middle- and high-income countries and used inconsistent measurement tools, our results may have some bias. Conclusions: The effects of social support in reducing suicide-related behaviors were positive, but it showed better effects in both female patients and adults. Males and adolescents deserve more attention. Future research needs to pay more attention to the implementation methods and effects of personalized social support.