Illicit substance use among third-level students is an issue of increasing concern. Digital behavioural change interventions have been developed to target this population, but reports of their effectiveness are mixed. The importance of end-user involvement in digital intervention development has been well established, but it appears that many interventions in this area did not engage end-users during development. This absence may have affected engagement, undermining their potential effectiveness. This paper describes the process and contributions of a persona-building approach in the development of a digital behaviour change intervention tailored to the needs of third-level students. Nine exploratory persona-building workshops were carried out with 31 students, and 7 project team members to develop personas for heavy, occasional and nonsubstance using third-level students. Early analysis has identified five archetypes which will contribute to the design of an acceptable and user-friendly intervention, and to the identification of targeted behavioural change techniques.