OBJECTIVE: To assess weight and HbA1c changes in the Healthier You: National Health Service Diabetes Prevention Programme (NHS DPP), the largest DPP globally to achieve universal population coverage. RESEARCH DESIGN AND METHODS: A service evaluation assessed intervention effectiveness for adults with nondiabetic hyperglycemia (HbA1c 42-47 mmol/mol [6.0-6.4%] or fasting plasma glucose 5.5-6.9 mmol/L) between program launch in June 2016 and December 2018, using prospectively collected, national service-level data in England. RESULTS: By December 2018, 324,699 people had been referred, 152,294 had attended the initial assessment, and 96,442 had attended at least 1 of 13 group-based intervention sessions. Allowing sufficient time to elapse, 53% attended an initial assessment, 36% attended at least one group-based session, and 19% completed the intervention (attended >60% of sessions). Of the 32,665 who attended at least one intervention session and had sufficient time to finish, 17,252 (53%) completed: intention-to-treat analyses demonstrated a mean weight loss of 2.3 kg (95% CI 2.2, 2.3) and an HbA1c reduction of 1.26 mmol/mol (1.20, 1.31) (0.12% [0.11, 0.12]); completer analysis demonstrated a mean weight loss of 3.3 kg (3.2, 3.4) and an HbA1c reduction of 2.04 mmol/mol (1.96, 2.12) (0.19% [0.18, 0.19]). Younger age, female sex, Asian and black ethnicity, lower socioeconomic status, and normal baseline BMI were associated with less weight loss. Older age, female sex, black ethnicity, lower socioeconomic status, and baseline overweight and obesity were associated with a smaller HbA1c reduction. CONCLUSIONS: Reductions in weight and HbA1c compare favorably with those reported in recent meta-analyses of pragmatic studies and suggest likely future reductions in participant type 2 diabetes incidence.