Objectives: To analyse service use and variation for people with severe mental illness in the last year of life in Wales. Methods: This is an observational retrospective cohort study between 2018 to 2023 using anonymised linked routinely collected health datasets within a data dashboard. Results: We identified n=4722 (2.3%) deaths with ICD-10 codes for severe mental illness for the period 2018-2023. As a group people with severe mental illness die younger, are in receipt of specialist palliative care at lower rates, die more often in institutional settings rather than their own homes and comorbidity indicates more unscheduled care use in the last year of life. Conclusions: Unscheduled care use in the last year of life is associated with comorbidity indicating opportunities for upstream intervention to improve treatment, experience and quality of life for people with severe mental illness. Further investigation such as mixed methodological approaches to examine experiences of those with severe mental illness in the last year of life, and the human and systems factors influencing the nature and effectiveness of unscheduled delivery for this patient cohort alongside developments in data linkage that include general practice, social care, nursing and specialist palliative care inputs are needed.