Depressive symptoms have been linked to the development of harmful drinking in adolescence but it remains unclear to what extent this effect continues into emerging adulthood. Deviant peers represent a risk factor while parental monitoring is a protective factor for harmful drinking. The study explored the relationship between depressive symptoms and harmful drinking between early adolescence and emerging adulthood. We also assessed to what extent this relationship is mediated by the influence of deviant peers and whether parental monitoring weakens this process. The sample consisted of 2964 adolescents (64 % females) from the Avon Longitudinal Study of Parents and Children study assessed between the ages of 14 and 19. Using structural equation modelling, we found that affiliation with deviant peers mediated the association between depressive symptoms and harmful drinking after adjustment for socio-demographic variables, parental drinking and depression, teenager’s sex, conduct problems as well as drinking and depressive symptoms in early adolescence. We also found that parental control and solicitation reduced the influence of deviant peers on harmful drinking. The results indicate that prevention programs should offer adolescents training for peer resistance training and monitoring skills training for parents may have a long-term effect at weakening peer influences on harmful drinking.