• Participant must be ≥ 18 years at the time of screening.

• Histologically- or cytologically-documented NSCLC and have been treated with concurrent CRT for locally advanced, unresectable (Stage III) disease

• Provision of a tumour tissue sample obtained prior to CRT

• Documented tumour PD-L1 status ≥ 1% by central lab

• Documented EGFR and ALK wild-type status (local or central).

• Patients must not have progressed following definitive, platinum-based, concurrent chemoradiotherapy

• Participants must have received at least 2 cycles of platinum-based chemotherapy concurrent with radiation therapy

• 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.

• WHO performance status of 0 or 1 at randomization

⁃ Adequate organ and marrow function