Abstract: Suicide is a widespread public health concern, including among military Veterans. Traumatic brain injuries (TBIs) and lack of social integration have both been shown to increase risk for suicidality, an outcome that includes, among other suicide-related variables, suicidal ideation, suicide attempts, and suicide death. Interestingly, TBIs have also been identified as a risk factor for social integration problems. In this cross-sectional study we investigated associations between TBI, social integration, and suicidality. Additionally, mediation analysis was used to test whether social integration mediated the association between TBI and suicidality. A sample of 1469 military Veterans (male, n = 1004, 67.2 %; female, n = 457, 32.3 %; transgender/non-binary/prefer not to say, n = 8, 0.5 %) completed an online survey as part of the Military Health and Well-Being Project. TBI was negatively associated with social integration (r = −0.084, p < .001) and positively with suicidality (r = 0.205, p < .001). Social integration was negatively associated with suicidality (r = −0.161, p < .001). Finally, social integration partially mediated the relationship between TBI and social integration (B = 0.121, 95 % CI [0.031–0.23]). This work shows that in the context of TBI, lack of social integration may promote suicidality. It provides support for many theories of suicide which propose social problems as a risk factor of suicide-related outcomes. It further highlights social integration as potential fodder for novel interventions for suicidality, an approach that would have transtheoretical support.