Overweight and obesity in youth with type 1 diabetes (T1D) is now prevalent and accounts for significant health consequences, including cardiovascular complications and dual diagnosis of type 2 diabetes. Physical activity and lifestyle are modifiable and play an important role in the prevention and management of excessive weight, but it is unclear how these factors relate to overweight and obese youth with T1D. Thus, a systematic review was conducted to examine how physical activity, sedentary behavior, sleep, and diet are related to overweight/obesity in youth with T1D. Seven observational and intervention studies published between 1990 and 2013 were included in the review. Prevalence of overweight ranged from 12.5% to 33.3%. Overweight in youth with T1D was associated with infrequent napping, increased screen time, and skipping breakfast and dinner but was not related to time engaged in physical activity. Weight-related interventions indicated modest weight loss along with improved glycemic control. In light of this review, there is a need for high quality research that examines all levels of activity in youth with T1D to identify lifestyle modification targets for weight prevention and management.