Aims: To investigate the combined association of adiposity and walking pace with incident type 2 diabetes. Methods: We undertook a prospective cohort study in 194 304 White‐European participants (mean age 56.5 years, 55.9% women). Participants' walking pace was self‐reported as brisk, average or slow. Adiposity measures included body mass index (BMI), waist circumference (WC) and body fat percentage (BF%). Associations were investigated using Cox proportional hazard models, with a 2‐year landmark analysis. A four‐way decomposition analysis was used for mediation and additive interaction. Results: The median (interquartile range) follow‐up was 5.4 (4.8‐6.3) years. During the follow‐up period, 4564 participants developed type 2 diabetes. Compared to brisk‐walking participants with normal BMI, those with obesity who walked briskly were at an approximately 10‐ to 12‐fold higher risk of type 2 diabetes (hazard ratio [HR] 9.64, 95% confidence interval [CI] 7.24‐12.84, in women; HR 11.91, 95% CI 8.80‐16.12, in men), whereas those with obesity and walked slowly had an approximately 12‐ to 15‐fold higher risk (HR 12.68, 95% CI 9.62‐16.71, in women; HR 15.41, 95% CI 11.27‐21.06, in men). There was evidence of an additive interaction between WC and BF% and walking pace among women, explaining 17.8% and 47.9% excess risk respectively. Obesity mediated the association in women and men, accounting for 60.1% and 44.9%, respectively. Conclusions: Slow walking pace is a risk factor for type 2 diabetes independent of adiposity. Promoting brisk walking as well as weight management might be an effective type 2 diabetes prevention strategy given their synergistic effects. [ABSTRACT FROM AUTHOR]