Background: People living in nursing homes face the risk of visiting the emergency department (ED). Outreach services are developing to prevent unnecessary transfers to ED. Aims: We aim to assess the performance of acute care services provided to people living in nursing homes or long-term homecare, focusing on ED transfer prevention, safety, cost-effectiveness and experiences. Materials & Methods: This review was guided by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Studies were eligible for inclusion if they were peer-reviewed and examined acute outreach services dedicated to delivering care to people in nursing homes or long-term homecare. The service models could also have preventive components. The databases searched were Scopus and CINAHL. In addition, Robins-I and SIGN checklists were used. The primary outcomes of prevented ED transfers or hospitalisations and the composite outcome of adverse events (mortality/Emergency Medical Service or ED visit after outreach service contact related to the same clinical condition) were graded with GRADE. Results: Fifteen relevant original studies were found—all were observational and focused on nursing homes. The certainty of evidence for acute outreach services with preventive components to prevent ED transfers or hospitalisations was low. Stakeholders were satisfied with these services. The certainty of evidence for solely acute outreach services to prevent ED transfers or hospitalisations was very low and inconclusive. Reporting of adverse events was inconsistent, certainty of evidence for adverse events was low. Conclusion: Published data might support adopting acute outreach services with preventive components for people living in nursing homes to reduce ED transfers, hospitalisations and possibly costs. If an outreach service is started, it is recommended that a cluster-randomised or quasi-experimental research design be incorporated to assess the effectiveness and safety of the service. More evidence is also needed on cost-effectiveness and stakeholders' satisfaction. Systematic review registration number: PROSPERO CRD42020211048, date of registration: 25.09.2020.