Diabetes mellitus (DM) is a complex endocrine disorder characterized by abnormally high levels of glucose, also called hyperglycemia. DM usually occurs when the body does not produce enough insulin or cannot respond to the insulin in the body. Type 1 diabetes mellitus (T1DM) or insulin-dependent diabetes is an autoimmune disease that affects around 8 million people in the world. Patients with T1DM experience an array of symptoms such as polyuria, polydipsia, and weight loss. These patients are prone to immediate life-threatening complications, including hypoglycemia and diabetic ketoacidosis. These patients are also at increased risk of ischemic heart disease, stroke, chronic kidney disease, vision loss, and even damage to nerve endings resulting in neuropathy. In this article, we will discuss type 1 diabetes mellitus and the different treatment options, focusing primarily on the Food and Drug Administration (FDA)-approved first cellular therapy for T1DM, donislecel.