A myasthenic crisis is a severe, life-threatening exacerbation of myasthenia gravis that causes a rapid onset of muscle weakness and fatigue that may result in tetraparesis, dyspnea, respiratory insufficiency, aspiration, and death. Bulbar muscle functions are markedly affected resulting in depressed cough reflex, swallowing, and speech. Thus, mechanical ventilation, supportive feeding, and critical care are essential for the survival of patients in a myasthenic crisis. Numerous precipitating factors of this condition are well known and include infections, various medications, pregnancy, and childbirth. Patients with myasthenia gravis are at a considerably higher risk of developing a debilitating coronavirus disease 2019 (COVID-19) infection due to the associated immunosuppression resulting from long-term corticosteroid use, which makes vaccination of such individuals necessary. However, the relationship between an exacerbation of myasthenia gravis and the COVID-19 vaccination is currently unknown. In this paper, we report the case of a 55-year-old male patient who developed a myasthenic crisis after receiving the first dose of the ChAdOx1-S (recombinant) vaccine (AstraZeneca batch number 210157; AstraZeneca plc, Cambridge, United Kingdom). Despite the administration of aggressive and intensive treatment over a period of 29-day hospitalization, the myasthenic crisis could not be reversed and the patient ultimately deteriorated and succumbed from multiple myocardial infarction events and organ failures. While it is still uncommon, evidence associating the effects of the vaccine to the development of a crisis is mounting; therefore, it is crucial for clinicians to promptly identify clinical features that suggest an exacerbation of myasthenia gravis in order to intervene at the earliest possible stage for a more favorable outcome. The myasthenia gravis patient should be informed about the possible association between COVID-19 vaccination and the development of a myasthenic crisis.