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

          -  Tumor PD-L1 expression

          -  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