Inclusive research involving people with intellectual disability is increasingly recognised. Although guidance exists, including a 2019 consensus statement on inclusive health research, the voices of people with intellectual disability are still often tokenistic or absent. This gap is especially critical in ageing research. In Australia, aged care policies define older age from 65 years. This threshold inadequately reflects the premature ageing and complex health needs experienced by people with intellectual disability, contributing to fundamental inequities. Informed by First Nations health policy approaches that recognise earlier ageing, a funded, mixed methods 'Healthy Ageing with Intellectual Disability' project seeks to inform more equitable access to health and aged care services through inclusive, policy-relevant research. This presentation describes a co-design approach, guided by a 2019 inclusive health research consensus statement, demonstrating how best practice co-design is being operationalised throughout the project rather than positioned as a symbolic add on. Codesign commenced prior to funding through deliberate efforts to understand the population, build trusted networks, and embed lived experience from the outset. A clinician-researcher with family lived experience of intellectual disability contributed to grant development and joined the project team following funding. A co-researcher with intellectual disability was recruited to a salaried role and supported to contribute across all project phases. Co-design informed project design, data access requests, and ethics applications, including development of stakeholder interview guides and advertising material. Steering, stakeholder, and co-design advisory groups are established to embed lived experience in all stages of decision making. Early embedded codesign enables rigorous, equitable healthy ageing research.