Abstract Background Existing evidence suggests that physical activity, in addition to medical treatment, can counteract physical symptoms and improve the quality of life in patients with inflammatory bowel disease (IBD). We aimed to understand patients' patterns of physical activity to guide the development of an evidence-based personalised intervention for the promotion of physical activity and reduction of sedentary behaviour in patients with IBD. Methods We included a population of 207,959 participants who responded to The Danish Capital Region Health Surveys during the period 2007 to 2021. The population included 1777 individuals with prevalent IBD [705 with Crohn’s disease and 1072 with ulcerative colitis]. Information on sedentary behaviour and physical activity was obtained from self-reported questionnaires, the Physical Activity Scale version 2.1., and sociodemographic information from central nationwide registers. Self-rated physical and mental health was measured with SF-12. Data were weighted for survey design and were analysed by multiple regression analyses. Results The proportion that adopted the recommended physical activity level of at least 4 hours of low, moderate, or high intensity was lower among patients with IBD compared to the background population, also when adjusting for sociodemographic variables and population weights (OR=0.86; 95% CI 0.84-0.88). Among patients with IBD, more women than men were physically active. Crohn’s disease, living alone, having non-western ethnicity, having a BMI< 18.5 or BMI >30, having an unhealthy diet, being outside the labour market, and having small children were all associated with lower levels of physical activity. Moderate to high level of physical activity among patients with IBD was associated with higher self-rated physical health than low levels of physical activity (p<0.001). The highest mental quality of life score was among IBD patients with moderate physical activity compared to high or low physical activity (p<0.001). Conclusion Patients with IBD, especially those with Crohn’s disease, have lower levels of physical activity and more sedentary behaviour compared to non-IBD individuals. Moderate physical activity is associated with a higher physical and mental quality of life score in individuals with IBD compared to high or low levels of physical activity. These results can guide clinicians when IBD patients ask for advice on physical activity. Furthermore, we will use the results to guide the development of an evidence-based personalised intervention for the promotion of physical activity and reduction of sedentary behaviour in patients with IBD.