Insulin derivatives provide new functions that are distinctive from native insulin. We investigated insulin modifications on the C-terminal A chain with insulin receptor (IR) peptide binders and presented a full and potent IR antagonist. We prepared insulin precursors featuring a sortase A (SrtA) recognition sequence, LPETGG, at the C-terminal A chain and used a SrtA-mediated ligation method to synthesize insulin derivatives. The insulin precursor exhibits full IR agonism potency, similar to native human insulin. We explored derivatives with linear IR binding peptides attached to the insulin C-terminal A chain. One insulin derivative with an IR binder (Ins-AC-S2) can fully antagonize IR activation by insulin, as confirmed by cell-based assays. This IR antagonist suppresses insulin-induced hypoglycemia in a streptozotocin-induced diabetic rat model. This study provides a new direction toward insulin antagonist development.