OBJECTIVES: There is growing appreciation of the role of community engagement and involvement (CEI) in designing context-specific interventions for individuals with acquired brain and spinal injuries (ABSI). This realist review evaluates CEI strategies in ABSI research in both high-income (HICs) and low- and middle-income countries (LMICs). DESIGN: A realist review. DATA SOURCES: Following RAMESES guidelines, a six-stage systematic search of the following databases: Medline, EMBASE, PsycINFO and Global Index Medicus was conducted from inception to March 2025. ELIGIBILITY: Studies assessing CEI in ABSI research design and implementation were included. Neurodegenerative pathologies and studies focusing solely on perspectives or attitudes were excluded. DATA EXTRACTION AND SYNTHESIS: Data were extracted and synthesised using context-mechanism-outcome configurations to explain how CEI strategies were used to improve outcomes. RESULTS: 22 studies were included. Data showed three context-specific focus areas in HICs and LMICs. In HICs prominent contexts were (a) low self-efficacy, (b) untailored rehabilitation services and (c) poor digital literacy. These were addressed through (a) recognising volitional barriers, (b) creating modular programmes and (c) end-user-tested tele-education tools. Whereas in LMICs, the data showed high rates of (d) stigma, (e) poor workforce capacity for community care and (f) barriers to accessible community support. These were addressed through (d) involving community champions, (e) task-shifting addressing workforce gaps and (f) state-level policy changes. Most common CEI interventions in both HICs and LMICs were community advisory boards, Delphi method and integrated knowledge-translation approaches. CONCLUSIONS: This study describes how different contextual factors affecting ABSI populations in HICs and LMICs interact with CEI strategies to trigger mechanisms that improve research engagement and patient outcomes. The study also highlights the dearth of CEI reported in neurosurgical trials. CEI should be embedded in experimental research to account for varying economic, social and infrastructural contexts, particularly in rural and LMIC settings.