Background: People with intellectual disabilities (ID) experience many health and social inequalities. Increasing physical activity is a proven intervention to address such inequalities, yet the physical activity rates of this population are substantially lower than the general population. Aim: Research has been growing to understand why this is and how to intervene to increase the physical activity levels of people with ID. Method: Using a behavioural epidemiological framework, the research in this area from barriers and facilitators of physical activity to translational research testing interventions within natural settings is reviewed. Findings from a total of 14 reviews and eight empirical studies and protocols were included. Results: Whilst there are multiple investigations into what promotes or enhances physical activity for people with ID, findings from intervention studies show few successful outcomes. Gaps within the existing research are identified and recommendations about how intervention efficacy might be improved are provided to inform future research and practice. Conclusion: Findings from previous research on barriers and facilitators can be further capitalised on and intervention studies should be underpinned by better links to theory and more systemic approaches.