Background Lifestyle interventions have been shown to improve physical function over the short term; however, whether these benefits are sustainable is unknown. The long-term effects of an intensive lifestyle intervention (ILI) on physical function were assessed using a randomized post-test design in the Look AHEAD trial. Methods Overweight and obese (body mass index ≥ 25 kg/m 2) middle-aged and older adults (aged 45-76 years at enrollment) with type 2 diabetes enrolled in Look AHEAD, a trial evaluating an ILI designed to achieve weight loss through caloric restriction and increased physical activity compared to diabetes support and education (DSE), underwent standardized assessments of performance-based physical function including a 4- and 400-m walk, lower extremity physical performance (expanded Short Physical Performance Battery, SPPB exp), and grip strength approximately 11 years postrandomization and 1.5 years after the intervention was stopped (n = 3,783). Results Individuals randomized to ILI had lower odds of slow gait speed (<0.8 m/s) compared to those randomized to DSE (adjusted OR [95% CI]: 0.84 [0.71 to 0.99]). Individuals randomized to ILI also had faster gait speed over 4- and 400-m (adjusted mean difference [95% CI]: 0.019 [0.007 to 0.031] m/s, p =.002, and 0.023 [0.012 to 0.034] m/sec, p <.0001, respectively) and higher SPPB exp scores (0.037 [0.011 to 0.063], p =.005) compared to those randomized to DSE. The intervention effect was slightly larger for SPPB exp scores among older versus younger participants (0.081 [0.038 to 0.124] vs 0.013 [-0.021 to 0.047], p =.01). Conclusions An intensive lifestyle intervention has modest but significant long-term benefits on physical function in overweight and obese middle-aged and older adults with type 2 diabetes. ClinicalTrials.gov Identifier NCT00017953.