The Nigerian Civil War (or Nigerian-Biafran War, 1967–1970) was fought between the Nigerian federal government and the defunct Republic of Biafra. Biafra recruited young men and boys (child soldiers) to fight the war, but little attention has been given to understanding the mental health outcomes of the War on Biafran veterans. Although there are few studies on social support in relation to post-traumatic stress disorder (PTSD) symptoms in this older veteran population, the mechanism through which social support influences PTSD has not received much attention. Hence, we investigated whether self-efficacy explains the association between social support and PTSD symptoms in a sample of Biafran War veterans. They were recruited from the Veterans’ association in south-east Nigeria ( N = 250; Mage = 71.33 years, SD = 7.11), and completed self-report measures of social support, self-efficacy, and PTSD symptoms. Results showed that veterans with greater social support (β = −.49, p < .001) and high self-efficacy reported less PTSD symptoms (β = −.55, p < .001). Above all, social support predicted decreased PTSD symptoms risk through increased self-efficacy, 95% CI [−0.53, −0.29]. By implication, social support may be associated with lower PTSD symptoms because it enhances efficacy beliefs, and thereby leads to less PTSD symptoms.