Emerging adulthood (ages 19 to 25) is a developmental phase that is marked by increased mental health conditions, especially depression and anxiety. A growing body of work indicates that digital peer emotional support has positive implications for the psychological functioning of emerging adults. These is burgeoning interest among healthcare professionals, educational stakeholders and policy makers in understanding the implementation and clinical effectiveness, as well as the associated mechanism of change, of digital peer support as an intervention. This randomized controlled trial (RCT) examined the effectiveness of digital peer support intervention over a digital platform-Acceset-for emerging adult psychological well-being with three primary aims. First, we evaluated the implementation effectiveness of digital peer support training for individuals providing support (befrienders), and digital platform for peer support. Second, we assessed the clinical outcomes of digital peer support, in terms of the intervening effect on emerging adult psychological well-being. Third, we investigated the mechanism of change linking digital peer support intervention to emerging adult psychological well-being. The RCT involving 100 emerging adults from the National University of Singapore follows the published protocol on this trial [29]. The RCT found effectiveness of digital peer support training-specifically, befrienders' peer support responses demonstrating significantly higher post- than pre-training scores in selfhood (post-training: M = 62.83, SE = 10.18; pre-training: M = 54.86, SE = 7.32), t(34) = 3.88, P < .0001. The digital peer support intervention demonstrated clinical effectiveness in enhancing selfhood, compassion and mindfulness, and in lowering depressive and anxiety symptoms among seekers in the intervention group at post intervention (M = 7.15, SE = 0.88) than seekers in the waitlist control group prior to intervention (M = 11.75, SE = 0.89), t(89) = 3.44, P = 0.0009. The effect of the intervention on seekers' psychological well-being was sustained beyond the period of the intervention. The mechanism of change revealed that seekers' engagement of the intervention had both immediate and prospective implications for their psychological well-being. This RCT on digital peer support intervention for emerging adult psychological well-being harnesses the interventional potential of four components of psychological well-being and elucidated a mechanism of change. By incorporating and validating the digital features and process of a peer support platform, our RCT provide the parameters and conditions in deploying effective and novel digital peer support intervention for emerging adult psychological well-being in real-world settings. ClinicalTrials.gov NCT05083676.