Difficulties in emotion regulation have been consistently associated with various psychological difficulties, including anxiety and depression; however, less is known about the directionality of this relationship, particularly in adolescents. In addition, early parent–child attachment quality has been closely linked to the development of emotion regulation. Previous studies have proposed an overarching model in attempt to describe the developmental trajectory of anxiety and depression from early attachment, albeit with several limitations that are discussed in this paper. This study adds to this field of research by investigating the longitudinal associations between emotion dysregulation (ED) and symptoms of anxiety and depression among 534 early adolescents in Singapore over three timepoints in a school year, and the antecedent role of attachment quality on individual differences on these variables. Bidirectional influences were found between ED and anxiety and depression symptoms, respectively, between T1 and T2, but not T2 and T3, at the between- and within-individual levels of analysis. Additionally, attachment anxiety and avoidance were both significantly predictive of individual differences in ED and for both psychological symptoms. The current findings provide preliminary evidence of a mutually reinforcing relationship between ED and symptoms of anxiety and depression in early adolescence, where attachment quality serves as a developmental antecedent that sets these longitudinal associations in motion.