Intellectual disability (ID), historically termed mental retardation, affects approximately 1–3% of the global population. Despite significant advances in diagnostic frameworks and rights-based care over the past two decades, substantial gaps remain in translating evidence-based policy into equitable practice, particularly in low- and middle-income countries where the majority of affected individuals reside. Objective: This multidisciplinary review synthesizes current evidence from clinical psychiatry, developmental psychology, special education, and social policy to propose an integrated, actionable model for assessment, intervention, and community participation for individuals with ID across the lifespan. A systematic narrative review was conducted using PubMed, PsycINFO, and Scopus for the period 2010–2025. Inclusion criteria were peer-reviewed articles in English addressing diagnosis (DSM-5/ICD-11), psychosocial interventions, family support, or community inclusion. Fiftyone key references were selected for thematic synthesis following a multistage screening process.Three major themes emerged from the (1) a fundamental diagnostic shift from IQ-centric classification to adaptive functioning and individualized support needs; (2) strong evidence for early behavioral and family-based interventions, though with significant implementation gaps; and (3) persistent, multi-level barriers to inclusive education, competitive employment, and accessible healthcare. Promising models identified include Community-Based Rehabilitation (CBR) and digital assistive technologies, yet both face scalability challenges.  A biopsychosocial-ecological framework is necessary to bridge the clinical-community divide. Future research must prioritize implementation science to adapt existing interventions for diverse cultural and resource contexts, as well as participatory methodologies that center the lived expertise of persons with ID. Policy reforms should mandate crosssectoral coordination with enforceable accountability mechanisms.