Aim To investigate the effectiveness of metformin in delaying or preventing progression to diabetes in a Chinese population with impaired glucose regulation (IGR). Materials and methods This multicentre, randomized, open-label, controlled study (NCT03441750) will assess the efficacy of metformin in preventing diabetes over >= 2 years. Eligible participants will be randomly assigned (1:1) to lifestyle intervention (LSI) or metformin plus LSI, with stratification based on blood pressure, anti-hypertensive medication use and isolated/non-isolated impaired fasting glucose. All participants will receive LSI advice. Participants in the metformin plus LSI group will receive metformin 850 mg once daily for the first 2 weeks, and twice daily thereafter, according to tolerability. Results The primary objective is to compare rates of newly diagnosed diabetes in the two intervention groups. Changes in glycaemia, blood pressure, body weight, insulin resistance, and safety outcomes will also be evaluated. Conclusions This large clinical trial in a Chinese population with IGR aims to provide critical information to guide clinical decision-making in order to alleviate the current diabetes epidemic.