Objective To assess the long-term effects of an intensive lifestyle intervention on physical function using a randomized post-test design in the Look AHEAD trial. Methods Overweight and obese (BMI ≥ 25 kg m-2) middle-aged and older adults (aged 45-76 years at enrollment) with type 2 diabetes (n = 964) at four clinics in Look AHEAD, a trial evaluating an intensive lifestyle intervention (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 an expanded short physical performance battery (SPPBexp), 20-m and 400-m walk, and grip and knee extensor strength 8 years post-randomization, during the trial's weight maintenance phase. Results Eight years post-randomization, individuals randomized to ILI had better SPPBexp scores [adjusted mean (SE) difference: 0.055 (0.022), P = 0.01] and faster 20-m and 400-m walk speeds [0.032 (0.012) m s-1, P = 0.01, and 0.025 (0.011) m s-1, P = 0.02, respectively] compared to those randomized to DSE. Achieved weight loss greatly attenuated the group differences in physical function, and the intervention effect was no longer significant. Conclusions An intensive lifestyle intervention has long-term benefits for mobility function in overweight and obese middle-aged and older individuals with type 2 diabetes.