The purpose of the study is to evaluate the efficacy and safety of tiragolumab plus atezolizumab compared with placebo plus atezolizumab in participants with previously untreated locally advanced, unresectable or metastatic PD-L1-selected non-small cell lung cancer (NSCLC), with no epidermal growth factor receptor (EGFR) mutation or anaplastic lymphoma kinase (ALK) translocation. Eligible participants will be randomized in a 1:1 ratio to receive either tiragolumab plus atezolizumab or placebo plus atezolizumab.

Inclusion Criteria:

• Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1
• Histologically or cytologically documented locally advanced or recurrent NSCLC not eligible for curative surgery and/or definitive radiotherapy with or without chemoradiotherapy, or metastatic Stage IV non-squamous or squamous NSCLC
• No prior systemic treatment for metastatic NSCLC
• High tumor tissue PD-L1 expression
• Measurable disease per Response Evaluation Criteria in Solid Tumors, Version 1.1 (RECIST v1.1)
• Adequate hematologic and end-organ function
• For participants enrolled in the extended China enrollment phase: current resident of mainland China or Taiwan and of Chinese ancestry.

Exclusion Criteria:

• Known mutation in the EGFR gene or an ALK fusion oncogene
• Symptomatic, untreated, or actively progressing central nervous system metastases
• 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
• Malignancies other than NSCLC within 5 years, with the exception of those with a negligible risk of metastasis or death treated with expected curative outcome
• Severe infection within 4 weeks prior to initiation of study treatment
• Positive test result for human immunodeficiency virus (HIV)
• Active hepatitis B or hepatitis C
• Treatment with investigational therapy within 28 days prior to initiation of study treatment
• Prior treatment with CD137 agonists or immune checkpoint blockade therapies, anti-CTLA-4, anti-TIGIT, anti-PD-1, and anti-PD-L1 therapeutic antibodies
• Treatment with systemic immunostimulatory agents within 4 weeks or 5 drug elimination half-lives prior to initiation of study treatment.

For eligible studies, qualified researchers may request access to individual patient level clinical data. See Roche's commitment to transparency of clinical study information here: https://go.roche.com/data\_sharing