Introduction Neutrophil‐to‐lymphocyte ratio (NLR) is a routinely available biomarker that reflects systemic inflammation. The study evaluated the predictive value of NLR for ischemic stroke and atrial fibrillation (AF) in patients with type 2 diabetes mellitus. Methods This was a population‐based cohort study of patients with type 2 diabetes mellitus and complete blood count tests at baseline between 1 January 1st, 2009, and 31 December, 2009, at government‐funded hospitals/clinics in Hong Kong. Follow‐up was until 31 December, 2019, or death. Results A total of 85,351 patients (age = 67.6 ± 13.2 years old, male = 48.8%, follow‐up = 3101 ± 1441 days) were included. Univariable Cox regression found that increased NLR at quartiles 2, 3 and 4 was significantly associated with higher risks of new‐onset ischemic stroke (hazard ratio HR: 1.28 1.20–1.37, p < .001, HR: 1.41 1.32–1.51, p < .001 and HR: 1.38 1.29–1.47, p < .001) and AF (HR: 1.09 1.02–1.17, p < .015; HR: 1.28 1.20–1.37, p < .001; HR: 1.39 1.31–1.49, p < .001) compared to quartile 1. On multivariable analysis, NLR remained a significant predictor of ischemic stroke risk for quartiles 2 and 3 (quartile 2: HR: 1.14 1.05, 1.22, p = .001; quartile 3: HR: 1.14 1.06, 1.23, p < .001) but not quartile 4 (HR: 1.08 0.994, 1.17, p = .070). NLR was not predictive of AF after adjusting for confounders (quartile 2: HR: 0.966 0.874, 1.07, p = .499; quartile 3: HR: 0.978 0.884, 1.08, p = .661; quartile 4: HR: 1.05 0.935, 1.16, p = .462). Conclusion NLR is a significant predictor of new‐onset ischaemic stroke after adjusting for significant confounders in Chinese type 2 diabetes patients. NLR is a significant predictor of new onset ischaemic stroke but not AF after adjusting for significant confounders in diabetes melltius.