Early life stressors are associated with maladaptive social functioning in childhood and adolescence, but it is unclear whether and how the negative interpersonal effects of stress persist into adulthood. Daily diary surveys were used to examine young adults' social behavior and mood reactivity to social stressors as a function of experiences of early family adversity. Stressful early family environments predicted more daily reassurance seeking, but not aggression, withdrawal, or positive social behavior. Early family adversity also moderated the within‐person effects of social stressors on next‐day mood, such that individuals with high levels of adversity had elevated next‐day negative affect in response to higher than average social stress. Findings highlight the enduring impact of early adversity on social development, with implications for developing targeted policies and interventions.