Being overweight or obese can have severe negative psychological impacts and reduce health-related functioning. To improve health-related quality of life (HRQoL) and sleep habits for children with overweight or obesity, it is important to design and implement effective interventions. The aim of this study was to evaluate the effects of a 6-month family-based lifestyle intervention on HRQoL and sleep habits in Norwegian children with overweight or obesity in a primary-care setting. This 6-month, non-randomised, cluster-controlled trial included Norwegian children aged 5–13 years with overweight or obesity and their parents. A questionnaire was filled out by the parents. A total of 33 and 52 children in the control group and 41 and 78 children in the intervention group answered the HRQoL and sleep habits questions, respectively, and were included. The intervention group received individual family counselling and participated in physical activity groups and nutrition courses. The Children’s Sleep Habits Questionnaire (CSHQ) and Kidscreen-10 index were used to assess sleep habits and HRQoL. At baseline, the mean average scores for HRQoL were 50.0 [standard deviation (SD) 8.1] for the intervention group and 49.0 (SD 10.1) for the control group. For sleep habits at baseline, the mean average scores were 45.2 (SD 11.8) for the intervention group and 46.0 (SD 11.9) for the control group. No significant changes in HRQoL and sleep habits after the intervention were revealed. Overall, the family-based lifestyle intervention targeting overweight and obese children in a primary-care setting showed no significant effect on HRQoL or sleep quality.