Art is increasingly being used by researchers as a medium to engage the public, yet evaluating and capturing impact remains challenging. We report an evaluation of a four-year public engagement project, I:DNA, designed to engage the public with research that explores the views and experiences of people with genetic conditions. An immersive art installation was exhibited at six scientific/cultural venues (2019–22), alongside several supplementary engagement activities, including talks, a game, ‘invisible theatre’, poetry workshops/performance and children’s art workshops. I:DNA reached over 26,500 people (online and in-person), and 268 people left some form of evaluation via postcards, online forms or emails. Through thematic analysis of this evaluation data, as well as the artistic outputs of supplementary activities, evidence of impact was identified in three key areas: changing views, inspiring behaviour change and supporting capacity for future public engagement. Implementation and evaluation of I:DNA highlights the challenges of evaluating the impact of complex arts-based public engagement projects, and the urgent need for methodological development to evaluate the processes by which impact occurs (not just the consequences of that impact), and the significance of venue and context, as well as the short-, medium- and long-term impacts of arts-based public engagement for both public and stakeholder groups.