A Safety Study of Oral Venetoclax in Combination With Intravenous Pembrolizumab in Adult Participants With Previously Untreated Non-Small Cell Lung Cancer (NSCLC) With High Programmed Cell Death Ligand-1 (PD-L1) Expression

Inclusion Criteria:

* Histologically documented advanced or metastatic NSCLC with no known epidermal growth factor receptor (EGFR) sensitizing (activating) mutation or anaplastic lymphoma kinase (ALK) translocation.
* At least one measurable lesion as defined by Response Evaluation Criteria in Solid Tumours (RECIST) 1.1.
* High PD-L1 tumor expression (tumor proportion score \>= 50%) as determined by a Food and Drug Administration (FDA)-approved test.
* Willing to provide tissue biopsy sample prior to start of study.
* Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1.

Exclusion Criteria:

* Received prior systemic treatment for their advanced or metastatic NSCLC. Participants who received adjuvant or neoadjuvant therapy are eligible if the adjuvant/neoadjuvant therapy was completed at least 6 months prior to the diagnosis of metastatic disease.
* History of or ongoing interstitial lung disease or pneumonitis that required oral or intravenous (IV) steroids.
* Active autoimmune disease that has required systemic treatment in past 2 years (i.e., with use of disease modifying agents, corticosteroids or immunosuppressive drugs). Replacement therapy (e.g., thyroxine, insulin, or physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency, etc.) is not considered a form of systemic treatment.
* Active severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. If a participant has signs/symptoms suggestive of SARS-CoV-2 infection, they should undergo molecular (e.g., polymerase chain reaction \[PCR\]) testing to rule out SARS-CoV-2 infection.