Early-onset type 2 diabetes mellitus is a rare condition and is often associated with genetic factors and complex comorbidities. Patients with this condition can show various complications, including early-age diabetic nephropathy which can cause significant clinical and social problems. This case report aims to evaluate the case of a 49-year-old patient with early-onset type 2 diabetes mellitus with diabetic nephropathy, mental retardation, and a family history of metabolic disorders who received family-based therapy. We report a male 49-year-old patient with early-onset type 2 diabetes mellitus diagnosed when the patient was 15 years old. Upon home visit, he was found to have uncontrolled blood glucose (289 mg/dl) with a BMI was 20.45 kg/m2 and blood pressure of 140/90 mmHg. Diabetic nephropathy was reported at the age of 44 years with persistent albuminuria and decreased glomerular filtration rate progressively. A history of type 2 diabetes mellitus and hypertension in the patient's father, mother, and grandmother. The patient was also diagnosed with mild mental retardation that did not receive treatment. The Caregiver Burden Scale (CGBS) assessment showed a moderately heavy burden on caregivers in managing patients. Family medicine intervention with education on diet patterns, physical activity, medication compliance, and stress management in caregivers was carried out. Intervention 3 times in 1 month showed improvement in patient blood glucose levels to 110 mg/dL and blood pressure level of 140/80mmHg. In conclusion, the family medicine approach intervention can improve patient glycemic control and provide comprehensive care to patients and their families, which eventually facilitates positive outcomes for diabetic nephropathy.