Acknowledgement of wider socio-ecological factors that influence dietary behaviours needs greater consideration in nutrition research with young people. Additionally, children and adolescents have a right to have their voices heard in research that concerns them. The aim of this methods paper is to describe and evaluate participatory methodologies undertaken as part of a dietary behaviour study with adolescents in the school setting in Ireland. Photovoice and peer-led focus groups were the key participatory methodologies, undertaken alongside food diaries and anthropometry. These methodologies were evaluated through discussion with peer researchers, qualitative surveys and in the context of the wider study process and outcomes. Peer researchers reported learning new skills including research, facilitation, listening and social skills and many felt they gained confidence, as well as an awareness about healthy and unhealthy practices at school. The findings were found to be authentic according to students, except for two limitations. Students believed body image was not adequately represented in the findings, and alternative focus group compositions could have influenced discussion content. Youth participants were afforded genuine opportunities to have their voices heard as part of a diet and nutrition research and the methodologies were acceptable and enjoyable. They demonstrated agency in valuable contributions at project design, data collection, analysis and interpretation stages of the research process. Furthermore, the participatory methodologies complemented quantitative data by providing environmental, behavioural, and socio-cultural insights into food choice in the school setting.