Tirzepatide is a once-weekly GIP/GLP-1 receptor agonist. In this phase 3, randomized, open-label trial, insulin-naive adults (≥18 years of age) with type 2 diabetes (T2D) uncontrolled on metformin (with or without a sulphonylurea) were randomized 1:1:1:1 to weekly tirzepatide 5 mg, 10 mg or 15 mg or daily insulin glargine at 66 hospitals in China, South Korea, Australia and India. The primary endpoint was non-inferiority of mean change in hemoglobin A1c (HbA1c) from baseline to week 40 after treatment with 10 mg and 15 mg of tirzepatide. Key secondary endpoints included non-inferiority and superiority of all tirzepatide doses in HbA1c reduction, proportions of patients achieving HbA1c < 7.0% and weight loss at week 40. A total of 917 patients (763 (83.2%) in China) were randomized to tirzepatide 5 mg (n = 230), 10 mg (n = 228) or 15 mg (n = 229) or insulin glargine (n = 230). All doses of tirzepatide were non-inferior and superior to insulin glargine for least squares mean (s.e.) reduction in HbA1c from baseline to week 40: tirzepatide 5 mg, 10 mg and 15 mg, −2.24% (0.07), −2.44% (0.07) and −2.49% (0.07), respectively, and insulin glargine, −0.95% (0.07), with a treatment difference ranging from −1.29% to −1.54% (all P < 0.001). Proportions of patients achieving HbA1c < 7.0% at week 40 were greater in tirzepatide 5-mg (75.4%), 10-mg (86.0%) and 15-mg (84.4%) groups compared to insulin glargine (23.7%) (all P < 0.001). All tirzepatide doses led to superior body weight reduction at week 40: tirzepatide 5 mg, 10 mg and 15 mg, −5.0 kg (−6.5%), −7.0 kg (−9.3%) and −7.2 kg (−9.4%), respectively, compared to insulin glargine, 1.5 kg (+2.1%) (all P < 0.001). The most common adverse events with tirzepatide were mild to moderate decreased appetite, diarrhea and nausea. No severe hypoglycemia was reported. Tirzepatide demonstrated superior reductions in HbA1c versus insulin glargine in an Asia-Pacific, predominately Chinese, population with T2D and was generally well tolerated. ClinicalTrials.gov registration: NCT04093752.