Autistic children commonly experience mealtime difficulties; however, it is unknown what makes an effective transdisciplinary mealtime service for autistic children. This study used a realist evaluation framework to explore caregivers' and therapists' perceptions of the contexts, mechanisms and associated outcomes of a transdisciplinary mealtime management service for autistic children. Semi-structured interviews were conducted with six caregivers of autistic children engaged in a transdisciplinary mealtime service and 10 therapists providing the service, with interview data analysed using a realist evaluation approach. Four-context (child factors, family factors, therapist factors and institutional parameters), three-mechanism (transdisciplinary collaboration, child-centred approach and managing caregiver expectations) and two-outcome (impact on the child and impact on the caregiver) themes were identified. Findings highlighted that transdisciplinary collaboration, a child- and family-centred approach and managing caregiver expectations are key mechanisms providing a foundation for the development of evidence-based mealtime services for autistic children.