Individuals with intellectual disabilities are disproportionately represented in criminal justice systems and often face inequitable treatment shaped by professionals’ knowledge, attitudes, and institutional constraints. This study aimed to systematically synthesize qualitative evidence on criminal justice professionals’ views, experiences, and decision-making when working with offenders with intellectual disabilities. The process of qualitative synthesis of evidence based on a thematic synthesis method was performed in compliance with the recommendations of ENTREQ and on the basis of PRISMA 2020. Five electronic databases were searched to find qualitative and mixed-method studies that were published between 2021 and 2025. A total of 6 studies that included criminal justice professionals in custody, court-based, and community settings were included based on the criteria. The data were synthesized and extracted using line-by-line coding, descriptive themes development, and higher-order analytical themes development. There were four identified descriptive themes, which include knowledge and recognition of intellectual disability, perceptions of vulnerability and risk, organizational and systemic constraints, and emotional and ethical challenges. These were informed by three analytical themes, namely, inconsistent professional responses based on knowledge gaps, structural tensions between care, control, and justice, and systemic reliance on individual advocacy and adaptation. All six studies reported challenging issues with the identification of intellectual disability, which led to disjunctive decision-making and informal coping. The results have identified structural flaws in the training, policy, and structural provision that led to inconsistent and inequitable justice provisions. To enhance equitable and ethically sound reactions to offenders with intellectual disabilities, the standardized identification, professional training, and inter-agency cooperation have to be strengthened.