This study examines the role of moral disengagement in fostering engagement in aggression and violence through adolescence to young adulthood in accordance with a design in which the study of individual differences and of their relations is instrumental to address underlying intraindividual structures and process conducive to detrimental conduct. Participants were 345 young adults (52% females) who were followed across 4 time periods (T1 M age = 17 years to T4 M age = 25 years). The longitudinal relations among irritability, hostile rumination, and moral disengagement attest to a conceptual model in which moral disengagement is crucial in giving access to action to aggressive tendencies. Findings suggest that irritability and hostile rumination contributed to the development of each other reciprocally and significantly across time. While hostile rumination and moral disengagement significantly mediated the relation between irritability and violence, moral disengagement significantly mediated the relation between hostile rumination and violence.