["British Journal of Learning Disabilities, EarlyView. ", "\nABSTRACT\n\nBackground\nAdults with intellectual disabilities experience higher rates and earlier onset of dementia, however post‐diagnostic support within community intellectual disabilities services remains inconsistently structured. Existing approaches often emphasise information provision or ad hoc advice, with limited availability of clearly specified, manualised psychosocial interventions tailored to this population.\n\n\nMethods\nPOST‐ID was developed through a staged, iterative and co‐produced intervention development process aligned with Medical Research Council guidance. Qualitative findings from caregivers and wider stakeholder engagement informed intervention design. Six caregivers, family and paid participated in structured review cycles to refine session content, materials, and delivery within routine community intellectual disabilities services. The final intervention was fully specified using the Template for Intervention Description and Replication (TIDieR) checklist.\n\n\nFindings\nStakeholder feedback led to substantive refinements, including delivery across six structured sessions, prioritisation of emotional safety and identity preservation, and explicit focus on carer‐mediated behaviour change. A central intervention output is a co‐produced Dementia Support Plan, designed to translate facilitated discussions into consistent, day‐to‐day caregiving practices across settings. These processes resulted in a structured, manualised, behaviourally informed psychosocial intervention deliverable by existing community intellectual disabilities clinicians.\n\n\nConclusion\nPOST‐ID provides a clearly specified, behaviourally informed post‐diagnostic psychosocial intervention designed for implementation within routine intellectual disabilities services and is ready for feasibility and implementation testing.\n"]