Background: Parity of esteem means that end-of-life care for people with severe mental illness should be of equal quality to that experienced by all. Aim: To synthesise international, English language, research and UK policy and guidance relating to the organisation, provision, and receipt of end-of-life care for people with severe mental illness. Design: A mixed methods systematic review was conducted following the Evidence for Policy and Practice Information and Co-ordinating Centre approach and informed by a stakeholder group. We employed thematic synthesis to bring together data from both qualitative and quantitative studies, and from non-research material. We assessed the strength of synthesised findings using the Confidence in the Evidence from Reviews of Qualitative Research (CERQual) and Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approaches. Data sources: Ten electronic databases were searched from inception to December 2019, along with 62 organisational websites. Quality appraisal was conducted using Critical Appraisal Skills Programme checklists or other study design-specific alternatives as necessary. Results: Of the 11,904 citations retrieved, 34 research publications were included plus 28 non-research items. The majority of research was of high or acceptable quality. An overarching synthesis including 52 summary statements, with assessments of confidence in the underpinning evidence, was produced using four themes: Structure of the system; Professional issues; Contexts of care; and Living with severe mental illness. Conclusions: Implications for services and practice reflect evidence in which there is a high degree of confidence. Partnership should be developed across the mental health and end-of-life systems, and ways found to support people to die where they choose. Staff caring for people with severe mental illness at the end-of-life need education, support and supervision. End-of-life care for people with severe mental illness requires a team approach, including advocacy. Proactive physical health care for people with severe mental illness is needed to tackle problems of delayed diagnosis.