Stage III non-small-cell lung cancer (NSCLC) represents a heterogeneous group of disease entities with multimodality treatments. For most patients, platinum-based doublet with concurrent chemoradiotherapy (CRT) has become the first-choice treatment over the past decade. Immune checkpoint inhibition has revolutionized the management of metastatic NSCLC; however, no major advances in systemic therapy for Stage III NSCLC have been made. The following report is the case of a patient with unresectable Stage IIIA NSCLC successfully treated with durvalumab. The patient completed 1 year of treatment without interruptions, and disease control has been maintained for more than 20 months since the start of durvalumab.