Veterans with combat exposure experience high rates of posttraumatic stress symptoms (PTSS) and associated suicidal ideation. The current study examined whether social support (i.e., social connectedness and social engagement) and protective psychological factors (i.e., resilience and altruism) moderated the relation between PTSS and suicidal ideation severity in a sample of 149 U.S. military combat veterans who served in the Vietnam War or Operation Enduring Freedom/Operation Iraqi Freedom/Operation New Dawn (OEF/OIF/OND). Consistent with expectations, initial PTSS were positively associated with concurrent and three-year follow-up severity of suicidal ideation. Moderation analyses revealed the relation between initial PTSS and concurrent suicidal ideation severity was no longer significant at above average levels of social connectedness, social engagement, and psychological resilience. Further, the relation between initial PTSS and suicidal ideation severity three years later continued to be buffered by above average levels of social engagement. Results suggest social connectedness, psychological resilience, and social engagement help moderate initial severe thoughts of suicide linked to PTSS, while social engagement might be the strongest protective factor against severe suicidal ideation over time. Empirically-supported prevention and treatment efforts enhancing social engagement may help promote resilience to severe PTSS-related suicidal ideation among veterans from Vietnam and OEF/OIF/OND combat eras.