Background: To improve the quality of palliative care, six evidence-based tools were implemented in 10 care services specialised in care for people with intellectual disabilities. Contextual differences were taken into account by using a participatory action research approach. Method: The RE-AIM framework (Reach, Effectiveness, Adoption, Implementation and Maintenance) structured the evaluation. Data sources were online questionnaires completed by 299 professionals at baseline (response 45.2%) and 250 professionals after 2.5 years (35.1%), 11 semi-structured group interviews with 43 professionals, field notes and implementation plans. Results: A total of 767 professionals and 43 teams were reached. The effectiveness of the intervention was demonstrated in an improved knowledge of palliative care policy and increased competences among professionals. 79% of the professionals adopted tools in the toolbox. The participatory action research method was perceived as valuable in driving change. Conclusions: Improving palliative care needs a context-specific, flexible approach, with involvement of all stakeholders.