There are no effective intervention studies for people using substances who are at, or near, the end of their lives. The needs of this group of people have been consistently overlooked even within the literature that identifies marginalised groups of people in need of greater recognition in palliative and end-of-life care. The aims of the project were to: (i) determine what a new, co-produced, model of care should look like for people using substances needing palliative and end-of-life care, and (ii) establish whether the new model had the potential to improve people’s access to, and experience of, end-of-life care. This paper presents the development of the new approach to care. It was developed using participatory action research principles over a course of online workshops during the COVID-19 pandemic lockdown period in the UK. A theory of change that aims to inform future policy and practice development is presented. While the ambition of the research was stunted by the pandemic, the process of its development and dissemination of the model and its resources has continued. Response from participants highlighted the importance of this work, however, in this new field of policy and practice, preparatory work that engages a wide range of stakeholders is crucial to its success. This relationship building and topic engagement are major parts of implementation before more substantial and sustainable development goals can be met.