During adolescence, a secure parent–adolescent relationship promotes youths’ adjustment and psychological well-being. In this scenario, several studies have demonstrated the effectiveness of the CONNECT program, a 10-session, attachment-based parenting intervention that helps parents understand and reframe their parent–adolescent interactions, reducing adolescents’ insecure attachment and behavioral problems. Furthermore, recent years have witnessed a significant increase in the implementation of effective online versions of psychological interventions, emphasizing the opportunity for more agile and easier dissemination of evidence-based protocols. Therefore, this study aims to identify changes in adolescents’ attachment insecurity, behavioral problems, and parent–child affect regulation strategies, providing preliminary findings on an online, 10-session, attachment-based parenting intervention (eCONNECT). A total of 24 parents (20 mothers, 4 fathers; Mage = 49.33, SD = 5.32) of adolescents (Mage = 13.83 years, SD = 1.76, 45.8% girls) were assessed on their adolescents’ attachment insecurity (avoidance and anxiety) and behavioral problems (externalizing and internalizing), and on their affect regulation strategies in the parent–child interaction (adaptive reflection, suppression, and affect dysregulation) at three time points: before intervention (t0), after intervention (t1), and at a 2-month follow-up (t2). Mixed-effects regression models highlighted a reduction in adolescents’ internalizing problems (d = 0.11), externalizing problems (d = 0.29), and attachment avoidance (d = 0.26) after the intervention. Moreover, the reduction in externalizing problems and attachment avoidance remained stable at follow-up. Additionally, our findings highlighted a reduction in parent–child affect dysregulation. Results add preliminary evidence on the implementation suitability of an online attachment-based parenting intervention to change at-risk adolescents’ developmental trajectories by reducing attachment insecurity, behavioral problems, and parent–child affect regulation.