Background: Autonomy is a crucial component of self-determination, yet it is limited for Autistic individuals, especially those with co-occurring intellectual disabilities. We explored how professionals supported Autistic people with intellectual disabilities' autonomy. Materials and Methods: This qualitative study used a community-based participatory approach. Nine staff who worked within a post-secondary transition programme to support Autistic young adults with intellectual disabilities were interviewed. Data were analysed using reflexive thematic analysis. Results: The quality and depth of relationships between staff and Autistic adults with intellectual disabilities, and a safe, supportive environment, were critical to supporting autonomy. Staff also identified several skill areas that would benefit program participants to exert their autonomy, including self-advocacy, interoceptive awareness, working with others, and understanding choices. Conclusions: This crucial information for supporting autonomy for Autistic adults with intellectual disabilities provides a basis for enacting programme change to promote self-determination. Recommendations for staff and programme development are provided.