OBJECTIVES: People with mental illness may be vulnerable to decline in mental health and reduced physical activity because of the COVID-19 pandemic and associated restrictions. The aim of this study was to inform the design of physical activity interventions for implementation under these conditions to improve/maintain well-being and physical activity in this population. METHODS: People with mental illness who had participated in a physical activity program prior to the pandemic were invited to complete a survey about the impact of COVID-19 on mental health and physical activity and their preferences for engaging in a physical activity program under pandemic-related restrictions. RESULTS: More than half the 59 respondents reported worse mental health and lower physical activity during the pandemic. The preferred format for a physical activity program was one-on-one exercise instruction in-person in a park. Program components endorsed as helpful included incentivization, provision of exercise equipment and fitness devices, and daily exercise programs. About a third of the participants reported limitations in using technology for a physical activity program. CONCLUSIONS: In-person exercise support is preferred by people with mental illnesses during pandemic-related restrictions. Enablement strategies such as providing equipment and self-monitoring devices should be utilized; assistance may be needed to incorporate the use of technology in exercise programs.