Generalized pustular psoriasis (GPP) presents as a severe variant of psoriasis featuring painful, sterile pustules on red skin and can lead to life-threatening complications if left untreated. The disease course is typically unpredictable, with periods of improvement, followed by relapses over extended periods. Managing GPP flares is challenging due to their potential to endanger the patient's life, underscoring the need for treatments that are both fast-acting and highly effective in the case of severe and systematically ill GPP patients. We present a case of a 48-year-old man with an extensive and severe GPP flare (GPP Physician Global Assessment score = 4), experiencing an extensive pustular rash on an erythematous base, intense skin exfoliation, and inflammation as well as systemic symptoms such as fever, hypotension, and general weakness. During the disease course, he developed comorbidities such as depression occurrence and an episode of an acute pulmonary embolism. Initial treatment attempts with acitretin and anakinra were not proved successful. Due to IL-36's significant role in GPP pathophysiology, the patient received treatment involving an IL-36 receptor antagonist (two infusions of 900 mg spesolimab administered one week apart), alongside continued acitretin therapy. This approach led to swift improvement, resolving pustules and skin inflammation and resulting in the patient's gradual recovery. This case highlights spesolimab's potential as a targeted therapy for severe GPP flares resistant to conventional treatments. However, further research is needed to establish its long-term safety and efficacy in managing GPP and related IL-36-mediated diseases.