Background: The importance of leisure sedentary behavior (LSB) change in diabetes prevention efforts is not well known. This study examines the relationships between changes in self-reported LSB and the primary intervention goals (weight and moderate-intensity to vigorous-intensity physical activity [MVPA]) during a community-based translation of the Diabetes Prevention Program (the Group Lifestyle Balance Program). Methods: A total of 322 adults at risk for type 2 diabetes were recruited from 3 community centers, a worksite, and military site. Community and worksite participants were randomized to immediate or delayed-delivery (control) intervention. All military site participants (n = 99) received immediate intervention. Logistic and linear generalized estimating equations were used to determine associations between LSB changes and weight-related outcomes and MVPA. Results: Results were obtained for 259 (80.4%) participants. The LSB decreased after 6 and 12 months (mean [95% confidence interval]: −25.7 [−38.6 to −12.8] and −16.1 [−28.2 to −3.9] min/d; both P < .05). Each 20-minute reduction in LSB was associated with a 5% increase in odds of meeting the weight-loss goal (6 mo: odds ratio = 1.05 [1.002 to 1.102]; P = .042; adjusted model including MVPA), but LSB was not related to changes in reported MVPA minutes or MVPA goal achievement. Conclusion: Within the context of existing lifestyle intervention programs, reducing sedentary behavior has the potential to contribute to weight loss separately from reported MVPA improvement.