Background Overweight and obesity are major health risk factors in people with intellectual disabilities. The aim of this study was to test the effectiveness of a multicomponent programme (physical activity, diet and motivation) for overweight and obesity in adults with intellectual disabilities. Material and Methods A quasi‐experimental design with repeated‐measures and non‐equivalent control group (n = 33, n = 31) was used. The programme was conducted over 17 weeks, with follow‐up at 6 months in a sample of Spanish adults with a mild and moderate intellectual disability from a community occupational day centre, aged from 23 to 50, 40.6% of which were women. Results A significant reduction in weight and diastolic blood pressure was obtained over time, and this reduction was maintained in the follow‐up for weight. Reduction in heart rate was only marginally significant. Conclusions The treatment was effective in reducing overweight and obesity, improving cardiovascular capacity and therefore the physical health of the participants.