Objective. Self-harm is associated with violent offending. However, little is known about young people who engage in “dual-harm” behavior. We investigated antecedents, clinical features, and life characteristics distinguishing dual-harming adolescents from those who self-harm only. Method. Participants were from the Environmental Risk (E-Risk) Longitudinal Twin Study, a nationally-representative UK cohort of 2,232 twins born in 1994-1995. Self-harm in adolescence was assessed through interviews at age 18. Violent offending was assessed using a computer questionnaire at age 18 and police records through age 22. Risk factors were assessed between ages 5-12. Adolescent mental health, victimization, personality functioning, and use of support services were measured at age 18. Results. Self-harm was associated with violent crime (OR=3.50, 95% CI=2.61-4.70), even after accounting for familial risk factors. Dual-harmers had been victims of violence from childhood, and exhibited lower childhood self-control and lower childhood IQ than self-only harmers. Dual-harmers experienced higher rates of concurrent psychotic symptoms and substance dependence. They also exhibited distinct personality styles characterized by resistance to change and by emotional and interpersonal lability. However, dual-harmers were not more likely than self-only harmers to have contact with mental health services. Conclusions. Dual-harmers have self-control difficulties and are immersed in violence from a young age. A treatment- rather than punishment-oriented approach is indicated to meet these individuals’ needs. Connecting self-harming adolescents with delinquency-reduction programs and transdiagnostic approaches that target self-regulation may reduce harmful behaviors. Preventing childhood maltreatment and implementing strategies to reduce victimization exposure could mitigate risk for both internalized and externalized violence.