Background: The COVID-19 pandemic has had a negative impact on the mental health of people with intellectual and developmental disabilities. Numerous pandemic-related stressors experienced by people with intellectual and developmental disabilities may have impacted their ability to thrive, which has been linked to mental health outcomes. The current study examined the associations among COVID-19 stressors, thriving, and mental health problems among youth and adults with intellectual and developmental disabilities. Method: Caregivers of 159 people with intellectual and developmental disabilities between 12 and 35 years of age from Canada completed an online questionnaire. Results: A mediation analysis revealed that COVID-19 stressors were positively associated with mental health problems, and that thriving partially mediated this association. Conclusion: Our findings suggest that experiences of thriving may be an important target for mental health support for people with intellectual and developmental disabilities.