A Study of Atezolizumab and Tiragolumab Compared With Durvalumab in Participants With Locally Advanced, Unresectable Stage III Non-Small Cell Lung Cancer (NSCLC)

Inclusion Criteria:

1. Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1
2. Histologically or cytologically documented NSCLC with locally advanced, unresectable Stage III NSCLC of either squamous or non-squamous histology
3. Whole-body Positron Emission Tomography-Computed Tomography (PET-CT) scan, performed prior and within 42 days of the first dose of concurrent chemoradiotherapy (cCRT)
4. At least two prior cycles of platinum-based chemotherapy administered concurrently with radiotherapy (RT), which must be completed within 1 to 42 days prior to randomization in the study (one cycle of cCRT is defined as 21 or 28 days)
5. The radiotherapy (RT) component in the cCRT must have been at a total dose of radiation of 60 (±10 percent [%]) gray (Gy) (54 Gy to 66 Gy) administered by intensity modulated RT (preferred) or 3D-conforming technique
6. No progression during or following concurrent platinum-based CRT
7. A known PD-L1 result
8. Life expectancy >/= 12 weeks
9. Adequate hematologic and end-organ function
10. Female participants must be willing to avoid pregnancy for 90 days after the final dose of tiragolumab and 5 months after the final dose of atezolizumab, or for 3 months after the final dose of durvalumab
11. Male participants must remain abstinent or use a condom during the treatment period and for 90 days after the final dose of tiragolumab
12. Male participants must not donate sperm during the treatment period and for 90 days after the final dose of tiragolumab

Exclusion Criteria:

1. Any history of prior NSCLC and/or any history of prior treatment for NSCLC (participants must be newly diagnosed with unresectable Stage III disease)
2. NSCLC known to have a mutation in the epidermal growth factor receptor (EGFR) gene or an anaplastic lymphoma kinase (ALK) fusion oncogene
3. Any evidence of Stage IV disease
4. Treatment with sequential CRT for locally advanced NSCLC
5. Participants with locally advanced NSCLC who have progressed during or after the definitive cCRT prior to randomization
6. Any Grade >2 unresolved toxicity from previous CRT
7. Grade >= 2 pneumonitis from prior CRT
8. Active or history of autoimmune disease or immune deficiency
9. History of idiopathic pulmonary fibrosis, organizing pneumonia, drug-induced pneumonitis, or idiopathic pneumonitis or evidence of active pneumonitis
10. History of malignancy other than NSCLC within 5 years prior to screening with the exception of malignancies with a negligible risk of metastasis or death
11. Prior allogeneic stem cell or solid organ transplantation
12. Active Epstein-Barr virus (EBV) infection or known or suspected chronic active EBV infection at screening
13. Treatment with investigational therapy within 28 days prior to initiation of study treatment
14. Prior treatment with CD137 agonists or immune checkpoint blockade therapies, including anti-cytotoxic T lymphocyte-associated protein 4, anti-T-cell immunoreceptor with Ig and ITIM domains (anti-TIGIT), anti-PD-1 and anti-PD-L1
15. Any prior Grade >/= 3 immune-mediated adverse event or any unresolved Grade > 1 immune-mediated adverse event while receiving any previous immunotherapy agent other than immune checkpoint blockade agents
16. Treatment with systemic immunosuppressive medication
17. Women who are pregnant, or breastfeeding