Snakebite envenomation is a life-threatening injury and a neglected public health issue in Africa. We report the case of a child that presented 6 days following a forearm snakebite with compartment syndrome and necrotizing fasciitis of the upper limb extending to the neck and chest who developed mediastinitis. She underwent multiple surgical debridements and the mediastinitis was managed non-surgically with antibiotics and postural drainage leading to recovery. The wounds were later grafted and the child discharged. Extension of necrotizing fasciitis from the limbs to the chest wall with development of mediastinitis is extremely rare with one previous case reported in a woman with poorly controlled diabetes mellitus on immunosuppressive therapy. We report this case due to its unusual presentation with no previous reports found on the development of mediastinitis following snakebite. In conclusion, physicians should have a high index of suspicion for mediastinitis in patients with necrotizing fasciitis extending to the neck and chest following snakebite.