This is a case of a 31-year-old male with no past medical history who developed extensive pulmonary embolism (PE) and deep venous thrombosis (DVT) three days after receiving the second dose of the Moderna vaccine. The patient presented with left calf swelling and mild shortness of breath, with no fever or hemodynamic instability. Doppler ultrasound of the left lower extremity showed thrombus in the common femoral, superior, mid-, and distal femoral, popliteal, and posterior tibial veins. Chest CT angiography (CTA) visualized extensive pulmonary emboli in the bilateral main pulmonary, lobar, and segmental arteries. Comprehensive hypercoagulable workup was unrevealing. The leading diagnosis was postulated as vaccine-induced thrombosis (VIT). Due to the diagnosis of bilateral sub-massive PE, the patient was initiated on enoxaparin and continued on direct-acting oral anticoagulation for at least one year. Our report showcases a plausible link between the Moderna vaccine and thrombosis due to the extensive and unprovoked nature of DVT/PE in this patient with a negative hypercoagulable workup. Although the mechanisms behind the messenger ribonucleic acid (mRNA) and double-stranded deoxyribonucleic acid (dsDNA) vaccines vary, the possibility of vaccine-induced thrombosis (VIT) after the Moderna vaccine is highly probable. Vaccine-induced thrombosis should be considered in a patient presenting with unprovoked thrombosis after the Moderna COVID-19 vaccine, and further research needs to be conducted to ascertain the correlation. However, these findings should not dissuade the use of the Moderna vaccine given its proven benefits.