Background and Objectives: This systematic review aimed to identify and appraise the evidence for online peer-support interventions for caregivers of stroke survivors (with and without aphasia), and people with dementia, traumatic brain injury (TBI), Parkinson's disease and multiple sclerosis. Research Design and Methods: Systematic review conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Five databases were systematically searched up until September 2020: EMBASE, PubMed, CINAHL, Scopus and Web of Science. Two reviewers independently screened titles, abstracts and full-text articles. The methodological quality of included studies was assessed using Physiotherapy Evidence Database (PEDro) and Mixed-Methods Appraisal Tool (MMAT) scales. Interventions were described using the Template for Intervention Description and Replication (TIDieR) checklist. Results: A total of 3026 records were identified from database searches. Following screening, 18 studies reporting 17 interventions were included in this review. Most studies (n = 13) reported interventions for caregivers of people with dementia. All studies incorporated an element of peer support as part of the intervention, however, most interventions (n = 15) comprised both psychosocial and educational elements. Statistically significant changes were reported for 11 interventions in one or more of the following domains: caregiver knowledge, mental health, stress, depression, distress, burden, self-efficacy, mastery, helplessness and perceived support. Qualitative outcomes included perceived reductions in stress and increased emotional and informational support. Discussion and Implications: Positive changes in caregiver outcomes were identified in response to multi-component online interventions (i.e., peer support in addition to education). Peer support was often poorly described, limiting the conclusions that could be drawn about the intervention components which result in better outcomes. Online interventions may provide an accessible and effective means of supporting caregivers.