To obtain a deeper understanding of peoples' experiences of cancer treatments with immune checkpoint inhibitors (ICIs). ICIs are transforming survival outcomes for many with certain advanced cancers. Given the possibility of unique immune-related adverse events (irAEs), understanding treatment experiences is crucial to identify support needs and provide safe and effective person-centred care. A systematic review of qualitative research and thematic synthesis. To report this review, the Preferred Reporting Items for Systematic Analysis and Meta Analysis (PRISMA) checklist and Enhancing Transparency in Reporting the Synthesis of Qualitative Research (ENTREQ) guidance have been used. MEDLINE, EMBASE, PsycINFO, CINAHL and Web of Science databases were searched in January 2022 for eligible studies published in English from database inception. Two reviewers independently screened records, identified papers for inclusion and appraised methodological quality using the Critical Appraisal Skills Programme checklist. Themes were developed using thematic synthesis. Eighteen papers were included and three analytical themes developed: immune checkpoint inhibitor treatment decision-making; the experience and impact of immune checkpoint inhibitor treatments; and appraising and responding to irAEs. The synthesis renders visible individuals' unmet information, psychological and practical support needs. It identifies shortcomings in immune checkpoint inhibitor treatment decision-making processes and highlights the need for healthcare professionals to recognise and sensitively handle individuals' treatment expectations. Individuals' understandings of and responses to irAEs are also illustrated, and attention drawn to patients' concerns about healthcare professionals' checkpoint inhibitor and irAEs knowledge. To sensitively manage treatment expectations and uncertainties, and optimise health outcomes, there are distinct points in treatment trajectories where care and support might require adapting and enhancing. This review addresses people's experiences of immune checkpoint inhibitor treatments. The core findings reveal unmet information, psychological and practical support needs. Insights derived from this review will enhance individuals' experiences and outcomes and healthcare professionals' practice. No patient or public involvement.