Expressive suppression is regarded as a generally ineffective emotion regulation strategy and appears to be associated with the development of depressive symptoms among adolescents. However, the mechanisms linking suppression to depressive symptoms are not well understood. The main aim of this study was to examine two potential mediators of the prospective relationship from depressive symptoms to expressive suppression among adolescents: parental support and peer victimization. Structural equation modelling was used to construct a three-wave cross-lagged model (n = 2,051 adolescents, 48.5% female, at baseline; 1,465 with data at all three time points) with all possible longitudinal linkages. Depressive symptoms preceded decreases in perceived parental support 1 year later. Decreases in parental support mediated the relationship between depressive symptoms and increases in expressive suppression over a 2-year period. Multi-group analyses show that the mediation model tested was significant for girls, but not for boys. No evidence for other mediating models was found. Although initial suppression preceded increases in depressive symptoms 1 year later, we did not find any evidence for the reversed link from suppression to depressive symptoms. Clear evidence for a reciprocal relationship between depressive symptoms and parental support was found. However, only limited and inconsistent support was found for a reciprocal relationship between depressive symptoms and peer victimization. Finally, although some evidence for a unidirectional relationship from parental support to increases in suppression was found, no significant prospective relationship was found between peer victimization and suppression. The implications of our clear results for parental support, and mostly lacking results for peer victimization, are discussed. (Contains 2 tables and 1 figure.)