We report a case of a 60-year-old lady who presented with bilateral lower limb swelling and a thyroid swelling with clinical features consistent with thyrotoxicosis. Investigations revealed the presence of a thrombus in bilateral external, internal iliac veins, and inferior vena cava extending up to its infrahepatic part. Hormone profile and radioiodine uptake scan confirmed the diagnosis of Graves' disease. Further workup revealed the presence of antiphospholipid antibodies (confirmed after a repeat test at 12 weeks). The patient was treated with antithyroid drugs and anticoagulants. The patient improved with normalization of thyroid function and partial recanalization of the infrahepatic part of inferior vena cava. Hyperthyroidism has been implicated as a potential hypercoagulable state; however, the association of Graves' disease with antiphospholipid antibody syndrome is limited to isolated case reports. This case highlights a new mechanism underlying hypercoagulability associated with Graves' disease.