Daily life with severe mental health (SMI) and cancer comorbidity entails multiple challenges. The study aims to explore everyday life experiences among individuals with SMI and cancer comorbidity from the perspectives of patients, significant others, and involved healthcare professionals. The study is registered in PROSPERO (CRD42021259604). A qualitative systematic review was conducted through searches in the databases MEDLINE, CINAHL, PsychInfo, and Web of Sciences (last search 14 February 2023). Inclusion criteria were empirical qualitative research studies investigating experiences of healthcare and everyday life among persons living with SMI and who were subsequently diagnosed with cancer from the perspective of the individuals themselves, their significant others, and healthcare professionals involved in their care. Exclusion criteria: Literature reviews, quantitative studies, intervention studies, quantitative parts of mix-methods studies, non-English languages, persons <18 years, dementia/learning disabilities, diagnosed with anxiety/depression as a consequence of cancer. Seven articles, published between January 2011 and February 2023, were included and analysed through a thematic analysis. The PRISMA 2020 checklist guided the study. The results were presented in four themes: ‘Navigating between different worlds and logics’, ‘Decision-making capacity depending on the assessor’, ‘Cancer must give way to severe mental illness or vice versa’, and ‘Significant others as a safety net’. Research about the everyday lives of persons with SMI and cancer comorbidities from patients’ and relatives’ perspectives is lacking and thus called for.