Autism Spectrum Disorder (ASD) is a multifactorial neurodevelopmental condition. ASD is characterized by impairments in social communication and repetitive behaviors. Increasing recognition of neurogenetic, immune, and metabolic underpinnings have spurned a plethora of therapeutic strategies. Despite advances in early behavioral interventions and symptomatic pharmacotherapy, no disease-modifying treatments exist. Stem cell therapy has emerged as an experimental approach, targeting the physiological and neurobiological constructs of ASD through mechanisms such as immunomodulation, neuroprotection, and metabolic support. The potent anti-inflammatory and neurotrophic effects of mesenchymal stem cells (MSCs) provide a novel strategy to address the pathophysiological underpinnings. MSCs have demonstrated safety and early efficacy in preclinical models and small clinical studies. Hematopoietic stem cells (HSCs) have also been investigated, particularly in subtypes of ASD associated with immune dysfunction. Preliminary trials suggest that both autologous and allogeneic stem cell infusions may improve core and associated ASD symptoms, though findings remain equivocal due to heterogeneity in patient populations, treatment protocols, and outcome measures. Meta- analyses suggest potential clinical benefit and minimal serious adverse events; however, the evidence base is limited by small sample sizes, short follow-up, and lack of standardized biomarkers or patient stratification strategies. Age, body size, and inflammatory status may also influence response, underscoring the need for personalized approaches. This review synthesizes the current preclinical and clinical literature on stem cell therapies in ASD, with emphasis on mechanistic rationale, treatment heterogeneity, and future directions for research. Larger, controlled trials are needed to clarify optimal stem cell sources, dosing regimens, and responder phenotypes, and to determine whether stem cell-based interventions can achieve durable functional improvements in ASD.