Aboriginal and Torres Strait Islander (hereafter ‘Aboriginal’) Australians experience higher risk of dementia and earlier onset than non Indigenous Australians. However, evidence on culturally appropriate interventions to prevent dementia in this priority population is limited. This study reports findings from a mixed methods process evaluation of Kaat Koort, a randomised controlled trial of an Aboriginal dementia prevention intervention conducted with Aboriginal communities in Western Australia, to inform culturally appropriate prevention strategies. Kaat Koort was implemented at two Aboriginal community controlled health services (one regional, one metropolitan) from 2021 to 2024, with 232 participants aged ≥35 years. A mixed methods process evaluation used the RE AIM framework (Reach, Effectiveness, Adoption, Implementation, Maintenance). Implementation data were obtained from the trial database (REDCap) and using project specific forms. Fifteen semi structured qualitative interviews were conducted with programme staff and trial participants (2024-2025). Quantitative data was summarised with descriptive statistics. Qualitative data was analysed using a combined inductive–deductive approach. Reach and adoption were driven by Aboriginal leadership, notably site specific champions who combined requisite skills with strong community networks. Proactive consistent engagement from intervention personnel, clear communications, a non-judgemental environment, flexibility and cultural tailoring were essential for successful implementation and participant retention. Several health behaviours were sustained in medium-term, indicating effectiveness and maintenance, to certain degrees. Major challenges included reliance on fewer key personnel – creating time constraints, study design elements that require further adaptation and COVID-related disruption. Aboriginal-led, culturally tailored, flexible lifestyle-based interventions delivered by engaging program personnel show promise. Meaningful co-design and reduced burden on champions may improve implementation and participant engagement.