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:

* Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1
* Histologically or cytologically documented NSCLC with locally advanced, unresectable Stage III NSCLC of either squamous or non-squamous histology
* Whole-body Positron Emission Tomography-Computed Tomography (PET-CT) scan, performed prior and within 42 days of the first dose of concurrent chemoradiotherapy (cCRT)
* 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)
* 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
* No progression during or following concurrent platinum-based CRT
* A known PD-L1 result
* Life expectancy \>/= 12 weeks
* Adequate hematologic and end-organ function
* 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
* Male participants must remain abstinent or use a condom during the treatment period and for 90 days after the final dose of tiragolumab
* Male participants must not donate sperm during the treatment period and for 90 days after the final dose of tiragolumab

Exclusion Criteria:

* Any history of prior NSCLC and/or any history of prior treatment for NSCLC (participants must be newly diagnosed with unresectable Stage III disease)
* NSCLC known to have a mutation in the epidermal growth factor receptor (EGFR) gene or an anaplastic lymphoma kinase (ALK) fusion oncogene
* Any evidence of Stage IV disease
* Treatment with sequential CRT for locally advanced NSCLC
* Participants with locally advanced NSCLC who have progressed during or after the definitive cCRT prior to randomization
* Any Grade \>2 unresolved toxicity from previous CRT
* Grade \>= 2 pneumonitis from prior CRT
* Active or history of autoimmune disease or immune deficiency
* History of idiopathic pulmonary fibrosis, organizing pneumonia, drug-induced pneumonitis, or idiopathic pneumonitis or evidence of active pneumonitis
* 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
* Prior allogeneic stem cell or solid organ transplantation
* Active Epstein-Barr virus (EBV) infection or known or suspected chronic active EBV infection at screening
* Treatment with investigational therapy within 28 days prior to initiation of study treatment
* 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
* 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
* Treatment with systemic immunosuppressive medication
* Women who are pregnant, or breastfeeding