Background: People with intellectual disabilities are rarely involved in end-of-life decisions. This study investigated and further developed approaches and resources to enable inclusive end-of-life care planning. Methods: A multi-centre, multi-method four-phase study, involving 195 researchers, participants, advisors and co-design members, including 36 people with intellectual disabilities: (i) evidence review; (ii) stakeholder focus groups; (iii) Experience-Based Co-Design and (iv) testing of co-designed resources. Results: There was little empirical evidence regarding the efficacy of existing resources. Focus group participants signalled overwhelming support for inclusive end-of-life care planning but notable variance around where/what/when/who/how. The co-design group developed a toolkit of existing and new resources. Feedback from toolkit testers was positive but barriers to staff engagement through the testing period were noted. Conclusions: Flexible, creative and interactive approaches that open up conversations are the building blocks for inclusive end-of-life care planning. Barriers include lack of staff confidence, time and resources and a death avoidance culture.