Background There is increasing evidence that active mobility contributes to overall physical activity, and is negatively associated with obesity. However, the associations between active mobility, physical activity and body weight are complex. In the current analysis, a number of research gaps are tackled (e.g. including leisure-time physical activity, ensuring a balanced and large enough sample size for different transport modes, a multicentre study in European cities). Methods The PASTA project recruited over 10,000 adults in 7 European cities (Antwerp, Barcelona, London, Oerebro, Rome, Vienna, Zurich) to complete a questionnaire on how they move around the city, their levels of physical activity, and sociodemographics. Self-reported use of different transport modes (“How often do you currently use each of the following methods of travel to get to and from places?”) was operationalized in eight categories: car, bike, e-bike, walk, bike and walk, motorcycle/moped, public transport, mixed. BMI was the dependent variable in multivariate linear regression models; models were sex-stratified; and city was included as random effect. Dominant transport mode was the primary exposure variable; daily car drivers were selected as the reference category. A number of important confounders were included in the analysis: age, days per week of moderate leisure physical activity, education level, household income, alcohol use, smoking, and self-rated health. Results The final sample size for the cross-sectional analysis was 10,562 (54% female, age 40 ± 13). In the models linking transport mode and BMI, we observed stronger relationships in men. A male daily cyclist versus a male daily car driver has a BMI that is on average 1.26 (95%CI 0.64-1.89) points lower, equivalent to 4 kg in our sample. For women, the difference was smaller and not statistically significant: 0.54 BMI points (95%CI -0.14-1.22) or 1.5 kg. In the full sample, we observed the largest difference in BMI for active modes (walking, cycling, and a combination) compared to daily car drivers, and a smaller difference for public transport (-0.58 BMI points; 95%CI -1.01-(-0.16)). People that combine active modes with motorized modes still have a lower BMI compared to only car drivers (-0.33 BMI points; 95%CI -0.79-0.13). Conclusions Men who drive cars as their main form of transport are on average 4kg heavier than those who cycle. In the future, we plan to investigate causality in a longitudinal study design by including results from a follow-up questionnaire reassessing BMI 1-2 years later in the same sample.