INCLUSION CRITERIA:  1. Participant must be ≥ 18 years at the time of screening. 2. Histologically- or cytologically-documented NSCLC and have been treated with concurrent CRT for locally advanced, unresectable (Stage III) disease 3. Provision of a tumour tissue sample obtained prior to CRT 4. Documented tumour PD-L1 status ≥ 1% by central lab 5. Documented EGFR and ALK wild-type status (local or central). 6. Patients must not have progressed following definitive, platinum-based, concurrent chemoradiotherapy 7. Participants must have received at least 2 cycles of platinum-based chemotherapy concurrent with radiation therapy 8. Participants must have received a total dose of radiation of 60 Gy ±10% (54 Gy to 66 Gy) as part of the chemoradiation therapy, to be randomised. Radiation therapy should be administered by intensity modulated RT (preferred) or 3D-conforming technique.  9. WHO performance status of 0 or 1 at randomization 10. Adequate organ and marrow function  EXCLUSION CRITERIA:  History of another primary malignancy except for malignancy treated with curative intent with no known active disease > 5 years before the first dose of study intervention and of low potential risk for recurrence, basal cell carcinoma of the skin, squamous cell carcinoma of the skin or lentigo maligna that has undergone potentially curative therapy, adequately treated carcinoma in situ or Ta tumours treated with curative intent and without evidence of disease. Mixed small cell and non-small cell lung cancer histology. Participants who receive sequential (not inclusive of induction) chemoradiation therapy for locally advanced (Stage III) unresectable NSCLC. Participants with locally advanced (Stage III) unresectable NSCLC who have progressed during platinum-based cCRT. Any unresolved toxicity CTCAE >Grade 2 from the prior chemoradiation therapy (excluding alopecia). Participants with ≥grade 2 pneumonitis from prior chemoradiation therapy. History of idiopathic pulmonary fibrosis, organizing pneumonia, drug-induced pneumonitis, or idiopathic pneumonitis, or evidence of active pneumonitis, ILD, pleural effusion, or pulmonary fibrosis diagnosed in the past 6 months prior to randomization. Active or prior documented autoimmune or inflammatory disorders (with exceptions) Active EBV infection, or known or suspected chronic active EBV infection at screening  Current or prior use of immunosuppressive medication within 14 days before the first dose of durvalumab.  Reproduction  Negative pregnancy test (serum) for WOCBP: Female participants must be 1 year post menopausal, surgically sterile, or using 1 highly effective form of birth control Male participants who intend to be sexually active with a WOCBP must be surgically sterile or using an acceptable method of contraception