Father involvement contributes uniquely to children's developmental outcomes. The antecedents of father involvement among unmarried, African American fathers from rural areas, however, have been largely overlooked. The present study tested a conceptual model linking retrospective reports of childhood trauma and early adulthood social instability to father involvement among unmarried, African American men living in resource-poor, rural communities in the southeastern United States. We hypothesized these factors would influence father involvement indirectly, via DNA methylation of the oxytocin receptor gene (OXTR). A sample of 192 fathers participated in 3 waves of data collection in early adulthood. Fathers reported on social instability at Wave 1; OXTR methylation was assessed via saliva samples at Wave 2; and measures of father involvement, retrospective childhood trauma, and quality of the fathers' relationships with their children's mothers were collected at Wave 3. Structural equation modeling indicated that childhood trauma was related directly to reduced levels of father involvement and to increased social instability. Social instability was associated with elevated levels of OXTR methylation, which in turn predicted decreased father involvement. The indirect effect from social instability to father involvement via OXTR methylation was significant. These associations did not operate through fathers' relationship with the child's mother and remained significant even accounting for associations between interparental relationship quality and father involvement. Findings suggest that OXTR methylation might be a biological mechanism linking social instability to father involvement among unmarried, African American fathers in vulnerable contexts and underscore the detrimental influence of childhood trauma on father involvement.