The International Classification of Functioning, Disability, and Health (ICF) is a framework designed by the World Health Organization (WHO) to help different sectors, such as healthcare, social services, education, and policy, understand how people with health-related issues function (do the things they want to and need to do) in their daily lives. This framework has also been used to guide clinical practice and research in autism and attention-deficit hyperactivity disorder (ADHD). To make it more practical, shorter versions of the ICF called Core Sets have been developed. We wanted to explore how the ICF and the ICF Core Sets have been used in research relating to autism and ADHD. We looked at the research that had been previously published on this topic by conducting a systematic search and review. Seventy-eight studies meeting our criteria were included in our review. Results show that the ICF has been applied in many ways across various contexts. However, most of the research has focused on autism, mainly involving children. The review highlights that although the ICF was used in some studies, the underlying philosophies of the framework were not always followed. The medical perspective still influenced the way research was done and interpreted. Nevertheless, using the ICF in the right way can help shift research on neurodevelopmental conditions like autism and ADHD toward a more holistic approach, moving away from solely focusing on medical aspects.