Background We investigated the effect of childhood maltreatment on predicting the 4‐year course of depressive and anxiety disorders and the possible mediating role of personality characteristics in the association between childhood maltreatment and illness course. Methods Longitudinal data in a large sample of participants with baseline depressive and/or anxiety disorders (n = 1,474, 18–65 years) were collected in the Netherlands Study of Depression and Anxiety. At baseline, childhood maltreatment was assessed with a semistructured interview. Personality trait questionnaires (Neuroticism–Extroversion–Openness Five Factor Inventory, Mastery scale, and Leiden Index of Depression Sensitivity), recent stressful life events (List of Threatening Experiences Questionnaire), and psychosocial variables were administered. The Life Chart Interview was used to determine the time to remission of depressive and/or anxiety disorders. Results At baseline, 846 participants (57.4%) reported any childhood maltreatment. Childhood maltreatment had a negative impact on psychosocial functioning and was predictive of more unfavorable personality characteristics and cognitive reactivity styles (P < 0.001). Childhood maltreatment was a significant predictor of lower likelihood of remission of depressive and/or anxiety disorders (HR = 0.94, P < 0.001). High levels of neuroticism, hopelessness, external locus of control, and low levels of extraversion were mediating the relationship between childhood maltreatment and 4‐year remission of depressive and anxiety disorders. Conclusions Certain personality characteristics are key players in the mechanism linking childhood maltreatment to an adverse illness course of depressive and anxiety disorders. Early interventions—reducing neuroticism and hopelessness, and enhancing extraversion and locus of control—might contribute to a better prognosis in a “high‐risk” group of depressive and anxiety disorders.