Adverse Childhood Experiences (ACEs) are key predictors of deliberate self‐harm (DSH). As part of the Northern Ireland Childhood Adversity Study (NICAS) we collected measures of self‐reported ACES (extended ACE‐IQ), DSH, mental health (anxiety, depression, stress), personality (behavioral inhibition, behavioral activation, mental toughness), resilience (Brief Resilience Score) and neurocognitive function (Iowa gambling test‐IGT‐ performance) in a sample of vulnerable young people aged 18–25 yrs (n = 122), and using Hierarchical Logistic Regression tested whether mental health, personality, resilience or neurocognitive function variables mediated the association between ACEs and DSH. The sample was characterized by a high mean rate of ACEs (5.29, SD = 3.00, range 0–13). Experience of 5 or more ACES (compared to those scoring <5 ) was by far the strongest predictor of DSH (OR: 23.35, CIs: 5.56, 83.02), with mental health (high vs low anxiety; OR: 5.1, CIs: 2.35–11.12 ) and personality (high vs low mental toughness; OR:4.18. CIs: 1.96, 8.91) also emerging as significant predictors of DSH. Both Advantageous vs disadvantageous performance on the IGT was also associated with DSH, but only at the NS trend (OR: 1.98, CIs:0 .94, 3.97, p = .07). We found no evidence to suggest associations between ACEs and DSH were mediated by mental health, personality or neurocognitive function variables. In the final model ACEs (OR:16.70, CIs: 4.51,61.8) and anxiety (OR:3.53, CIs: 1.45,61.8) remained; together accounting for 37% of the variation in DSH. The identification of targeted interventions and effective treatments for vulnerable young people at risk of DSH is essential.