© 2020 John Wiley & Sons, Ltd It is well established that stressful life events (e.g., family bereavements or moving to a new country) are damaging to psychological health and well-being. Indeed, social relationships are often noted as an important factor that can influence well-being and buffer the negative effects of stress. However, the quality and source of these relationships, particularly for adolescents, are often overlooked. Using the Growing Up in Ireland Survey, a population-based study of 13-year-old Irish adolescents (N = 7,525; 51.1% female), the current study examines the quality of both parent and peer relationships as potential mechanisms explaining the association between stressful life events and psychological well-being indices in adolescents. As expected, results showed that stressful life events negatively impacted the psychological well-being of adolescents. Parallel mediation analyses indicated that both parent and peer relationship quality mediated this association. Further exploratory analyses found that for girls, greater numbers of stressful life events were associated with poorer quality relationships with both their parents and peers, and in turn, these were linked to lower levels of psychological well-being. For boys, this effect was only evident for parental relationship quality, but not peers. The implication of these findings for adolescent's psychological well-being, particularly for girls, is discussed.