Pseudoaneurysm (PA) is a well-known vascular complication following percutaneous interventions, typically occurring in the early post-procedural period. However, delayed-onset PA associated with deep vein thrombosis (DVT) is an uncommon presentation. This case highlights a late external iliac artery (EIA) PA diagnosed in a patient who initially underwent coronary angiography. A 65-year-old male underwent a routine coronary angiography via the femoral artery and was discharged without complications. Twenty days later, he presented with unilateral lower limb swelling and pain. Doppler ultrasonography revealed extensive external iliac DVT, and contrast-enhanced computed tomography (CT) angiography confirmed a PA of the EIA. Endovascular stent graft placement was performed successfully. The patient was followed for 1 week, during which the limb swelling and pain resolved completely, and he was discharged without complications. This case underscores the importance of considering delayed PA formation in patients with unexplained limb swelling after arterial access procedures. Early diagnosis and intervention are crucial in preventing complications and ensuring favorable outcomes.