Integration of cognitive, sensory, and motoric processes is essential for the production of handwriting, however, challenging for children and youth with Autism Spectrum Disorder (ASD). The objective of this scoping review is to identify potential underlying mechanisms of handwriting of children and youth with ASD by reviewing cognitive, sensory, and motoric body functions as predictors of their handwriting. The International Classification of Functioning, Disability, and Health -- Children and Youth version was used to structure the analysis. Eleven studies (0.9%) met inclusion criteria. Results show that linguistic functions, psychomotor functions, motor control functions, and motor reflex functions predict handwriting of children and youth with ASD. This suggests these body functions are underlying mechanisms of handwriting of children and youth with ASD, encouraging future research to test these body functions as potential pathways to handwriting intervention for children and youth with ASD. Findings suggest a bottom-up approach to the development of handwriting interventions for children and youth with ASD.