AimTo identify, describe and synthesise what is known about family carers' experiences and perspectives of engagement in delirium prevention and care for adults in hospital.DesignSystematic review and synthesis of qualitative evidence.Data SourcesComprehensive literature search within PubMed, CINAHL, EMBASE, Scopus, Cochrane Central and PsycInfo databases to August 2022. Peer reviewed original qualitative research published in English.MethodsData were extracted using Covidence systematic review software. Methodological quality was reviewed against the Critical Appraisal Skills Program (CASP) Qualitative Checklist. Thematic synthesis was used to develop analytical themes. Confidence in the Evidence from Reviews of Qualitative Research (GRADE‐CERQual) framework was applied to findings.ResultsOf 3429 records identified, 29 met criteria for final inclusion. Studies included a range of settings (intensive care, medical and surgical wards) and family carer types (spouse, daughter, parent and friend). Three primary themes Shared Caregiving, Partnership and Support, Communication for Shared Understanding and three cross‐cutting contextual themes Care Transitions, Family Carer Context and Hospital Context were identified. Family carers have mixed experiences of involvement in delirium care and prevention. Family carer engagement in care impacted perceptions of care quality and their own self‐efficacy. Where person‐centred care expectations were not met, some family carers adopted compensatory or care contingency strategies. Information sharing and timely support from hospital staff who understood the carer context supported carer involvement. Supportive physical environments and addressing power imbalances allowed greater engagement.ConclusionFamily carers often wish to be involved in delirium prevention and care, but need to be recognised as individuals, listened to, informed and supported to optimise their contribution.ImpactThe review findings can guide health professional and decision makers to optimise family carer involvement in delirium care programs.Protocol RegistrationPROSPERO [CRD42020221854].ReportingENTREQ.No Patient or Public Contribution.