Introduction High body mass index (BMI) is associated with risk of diabetes. Lorcaserin is a selective 5-hydroxytryptamine 2C agonist which exerts robust benefits on long-term weight loss by suppressing appetite among adults with overweight or obesity. The magnitude of efficacy of lorcaserin for preventing and remitting type 2 diabetes mellitus (T2DM) among those people remains undefined. Therefore, we plan to conduct this systematic review and meta-analysis to aggregate data from all published studies with regard to the issue to acquire reliable evidence. Methods and analysis We will search various databases for relevant trials published up to June 2019. Randomised controlled trials investigating the efficacy of lorcaserin for preventing and remitting T2DM among overweight and obese population will be included. A standardised data form will be used to complete data search and extraction in duplicate. All discrepancies will be resolved by consensus. The primary outcome will be incidence of T2DM in patients with pre-diabetes. Secondary outcomes will include achievement of normoglycaemia in people with pre-diabetes, remission of hyperglycaemia in patients with diabetes, the proportion of patients with weight loss of at least 5% or 10% and hypoglycaemia incident. Data synthesis and statistical analysis will be performed for each outcome with Stata V. 14.0. Ethics and dissemination Ethics approval is not required. Results of our study will be submitted to a peer-review journal. PROSPERO registration number CRD42019119136.