Background: Justice systems globally face challenges due to pervasive engagement in antisocial behaviours, suggesting that further research on the causes of antisociality is needed. Life history (LH) influences the development of the Five-Factor Model (FFM) of personality, and both variables are strong predictors of antisociality. However, no research has yet assessed their joint impact. Objective: This study aimed to explore the direct and indirect effects of LH and the FFM on adult engagement in antisocial behaviours. Methods: An international sample of 490 adults (310 women, 173 men, 7 non-binary; M age = 41.19 years, SD = 1.13) responded to measurements of LH, FFM placements, and frequency of antisocial activity. Bootstrapped parallel mediation was employed to analyse the data. Results: The findings indicated that the FFM domains of conscientiousness, extraversion, agreeableness, and neuroticism fully mediated the relationship between LH and antisociality, suggesting the effect of LH is completely indirect. Conclusion: This study provides novel insights into an extended LH-FFM-antisociality model, which has important implications for upcoming LH research and development of programs rehabilitating adult antisociality, including the assessment and alteration of antisocial cognitive distortions and behaviour.