BACKGROUND: Adolescence is a developmental period during which an estimated 75% of mental health problems emerge (Solmi et al. in Mol Psychiat 27:281-295, 2022). This paper reports a feasibility study of a novel indicated, preventative, transdiagnostic, school-based intervention: Building Resilience Through Socioemotional Training (ReSET). The intervention addresses two domains thought to be causally related to mental health problems during adolescence: social relationships and emotion processing. Social relationships were targeted using principles from interpersonal psychotherapy, while emotion processing was targeted using cognitive-emotional training focused on three areas of emotion processing: Emotion perception, emotion regulation and interoception. The aims of this feasibility study were to (i) assess the acceptability of integrating group-based psychotherapy with individual cognitive-emotional training, (ii) evaluate the feasibility of our recruitment measures, and (iii) assess the feasibility of delivering our research measures. METHODS: The feasibility study involved 41 adolescents, aged 12-14, who were randomly assigned to receive the ReSET intervention or their school's usual mental health and wellbeing provision. RESULTS: Qualitative data from intervention participants suggested the programme was experienced as a cohesive intervention, with participants able to draw on a combination of skills. Further, the cognitive-training tasks were received positively (with the exception of the interoception training task). The recruitment and research measures were successfully delivered in the school-based setting, with 97.5% retention of participants from baseline to post-intervention assessment. Qualitative data was overwhelmingly positive regarding the benefits to participants who had completed the intervention. Moreover, there was only limited data missingness. CONCLUSIONS: We conclude that a trial of the ReSET intervention in a school setting is feasible. We discuss the implications of the feasibility study with regard to optimising school-based interventions and adaptations made in preparation for a full-scale randomised controlled trial, now underway.