Cervical necrotizing fasciitis (CNF) is a rare condition in the United States, with very few cases reported as a sequela of mandibular fracture. The authors describe the case of a 40-year-old man with poor oral health and no significant past medical history who developed CNF following delayed treatment of an open mandibular fracture, leading to life-threatening septic shock, thrombophlebitis of the internal jugular vein, and septic emboli to the lungs. Successful management of this patient was accomplished by serial surgical debridement, the administration of broad-spectrum antibiotics, and hemodynamic support. Eventual reconstruction was performed with external fixation of the mandible fracture and split-thickness skin grafting for the left neck and chest wound. The authors recommend early treatment of open mandibular fractures for immunocompromised patients or patients with poor oral hygiene to avoid the rare but potentially fatal complication of CNF and highlight external fixation as a useful technique in select cases of complex mandibular fractures.