Background: Adults with mild-moderate intellectual disabilities have difficulties in accessing traditional evidence-based health promotion initiatives despite experiencing health disparities; yet there are few studies with this group and their carers exploring how their needs can be met. Method: This study adapted a behaviour change theory-based approach to interview this group and their carers and ascertain if this method was feasible and appropriate to explore how healthier behaviour uptake could be improved amongst adults with intellectual disabilities. Results: A community-based, staged recruitment process and iterative approach to data collection and analysis supported successful participation amongst adults with intellectual disabilities in behaviour-change theory-based interview research. Methodological adaptations enabled richer data collection amongst adults with mild--moderate intellectual disabilities and carers. Conclusions: It is feasible and important to include adults with intellectual disabilities in qualitative health research that uses theory-based complex constructs to inform development of person-centred health promotion interventions with this underserved cohort.