Background: Canadian 24-h movement guidelines recommend that adults achieve 150 min per week of moderate-to-vigorous physical activity (MVPA), 7-9 h of sleep per night and spend no more than 8-h per day sedentary to optimise health and wellbeing. Method: Using a cross-sectional survey of 131 family caregivers of adults with intellectual and developmental disabilities, we aimed to (a) determine whether adherence to these guidelines predicts mental wellbeing in family caregivers and (b) explore the relationship between movement behaviours of family caregivers and their loved ones. Results: While MVPA was found to weakly predict wellbeing, sleep and sedentary behaviour did not. The movement behaviours of the family caregivers were not closely related to that of their loved ones. Conclusions: Fostering physical activity is important to promote the wellbeing of adults with intellectual and developmental disabilities, as well as their family caregivers. Opportunities to be active together may be even more beneficial.