Inclusion Criteria

• Participants must have a histologically- or cytologically-confirmed diagnoses of non-small cell lung cancer (NSCLC) with unresectable Stage III disease.
• Participants must have received at least 2 cycles of platinum-based concurrent chemoradiotherapy (a total dose of radiation of at least 54 Gy).
• Participants must have no progressive disease (PD) following treatment with concurrent chemoradiotherapy (CCRT).
• Participants must have an Eastern Cooperative Oncology Group (ECOG) performance status (PS) score of 0 or 1.

Exclusion Criteria

• Participants with non-squamous histology must not have documented Epidermal Growth Factor Receptor (EGFR) and anaplastic lymphoma kinase (ALK) rearrangements.
• Participants must not have an active autoimmune disease.
• Participants must not have significant cardiovascular impairment such as uncontrolled hypertension (despite optimal medical treatment), congestive heart failure, active coronary disease (within 6 months prior to randomization), ventricular arrhythmias, major thrombotic or embolic events or major hemorrhagic events within 6 months prior to randomization, or significant risk of pulmonary hemorrhage.
• Participants must not have advanced/clinically significant lung disease (within 6 months prior to randomization) or history of interstitial lung disease (ILD) or pneumonitis requiring treatment with systemic steroids (≥ Grade 2), or current or suspected ILD or pneumonitis.
• Participants must not have any prior anticancer therapy (outside of CCRT) for locally advanced Stage III disease.
• Other protocol-defined Inclusion/Exclusion criteria apply.