BACKGROUND: Out-of-hours (OOH) hospital admissions for patients receiving end-of-life care are a common cause of concern for patients, families, clinicians, and policymakers. It is unclear what issues, or combinations of issues, lead OOH clinicians to initiate hospital care for these patients. AIM: To investigate the circumstances, processes, and mechanisms of UK OOH services-initiated end-of-life care hospital admissions. DESIGN AND SETTING: Systematic literature review and narrative synthesis. METHOD: Eight electronic databases were searched from inception to December 2019 supplemented by hand-searching of the British Journal of General Practice. Key search terms included: 'out-of-hours services', 'hospital admissions', and 'end-of-life care'. Two reviewers independently screened and selected articles, and undertook quality appraisal using Gough's Weight of Evidence framework. Data was analysed using narrative synthesis and reported following PRISMA Complex Intervention guidance. RESULTS: Searches identified 20 727 unique citations, 25 of which met the inclusion criteria. Few studies had a primary focus on the review questions. Admissions were instigated primarily to address clinical needs, caregiver and/or patient distress, and discontinuity or unavailability of care provision, and they were arranged by a range of OOH providers. Reported frequencies of patients receiving end-of-life care being admitted to hospital varied greatly; most evidence related to cancer patients. CONCLUSION: Although OOH end-of-life care can often be readily resolved by hospital admissions, it comes with multiple challenges that seem to be widespread and systemic. Further research is therefore necessary to understand the complexities of OOH services-initiated end-of-life care hospital admissions and how the challenges underpinning such admissions might best be addressed.