Dual harm behaviour has recently gained scholarly attention. Dual harm centres on a subset of people who display violent and self-harming behaviour. This study re-examines the differential profile characteristics identified in Europe for those who dual harm, using international data featuring a population study of a state prison system in the south-eastern United States. Three years of data produced 43,489 institutional events, from a custodial population of 22,918. Logistic regression analysis indicates that those who dual harm in custody had an overall rate of infraction 40–70% higher than those who engage solely in violence or self-harm, and five times higher than those without physical harm infractions. Dual harm was associated with higher rates of non-harm incidents (e.g. property damage and disorder), younger age, lower educational achievements on admission and less educational development during imprisonment, greater self-reported mental health need although not substance abuse, and fewer intimate relationships. Dual harm was related to more lethal acts of self-harm such as ligature or ingestion. This is the first study that applies the dual harm profile to prison data within the US. This study supports dual harm as a highly relevant construct within international custodial settings and offers policy implications for this population.