Type 2 diabetes mellitus (T2DM) is a chronic metabolic disorder characterized by insulin resistance and progressive pancreatic β-cell dysfunction. Conventional biomarkers such as fasting plasma glucose and glycated haemoglobin (HbA1c) detect established disease but fail to capture early molecular alterations and future complication risk. Epigenetic biomarkers—including DNA methylation, histone modifications, and non-coding RNAs—are emerging as powerful, dynamic, and modifiable indicators of disease susceptibility and progression. These biomarkers not only enable early diagnosis and risk stratification but also hold promise in predicting major complications such as myocardial infarction, stroke, and diabetic kidney disease. This clinician-focused review summarizes current evidence on epigenetic biomarkers in T2DM, highlights key CpG sites, and discusses their diagnostic, prognostic, and therapeutic implications in precision medicine.