The main inclusion criteria include but are not limited to the following:

• Has histologically- or cytologically-confirmed diagnosis of Stage IV squamous or nonsquamous NSCLC
• Participants with nonsquamous NSCLC who are not eligible for an approved targeted therapy
• Is able to provide archival tumor tissue sample collected either within 5 years or within the interval from completion of last treatment but before entering the screening period or newly obtained core or excisional biopsy of a tumor lesion not previously irradiated obtained within 90 days of treatment initiation
• Has not received prior systemic treatment for their metastatic NSCLC
• Is able to complete all screening procedures within the 35-day screening window for Part A and 28-day screening window for Part B

The main exclusion criteria include but are not limited to the following:

• Has a diagnosis of small cell lung cancer
• Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy (in dosing exceeding 10 mg daily of prednisone equivalent) or any other form of immunosuppressive therapy within 7 days before the first dose of study treatment
• Has a known additional malignancy that is progressing or has required active treatment within the past 2 years
• Has known active central nervous system (CNS) metastases and/or carcinomatous meningitis
• Has an active autoimmune disease that has required systemic treatment in the past 2 years
• Has a history of (noninfectious) pneumonitis that required steroids or has current pneumonitis
• Has an active infection requiring systemic therapy
• Has clinically significant cardiac disease, including unstable angina, acute myocardial infarction within 6 months from Day 1 of study treatment administration, or New York Heart Association Class III or IV congestive heart failure
• Has a known history of human immunodeficiency virus (HIV) infection. Well-controlled HIV with anti-retroviral therapy (ART) is not excluded
• Has a known history of Hepatitis B (HPV) or known active Hepatitis C virus infection. Hepatitis B surface antigen (HBsAg) positive is eligible if on HBV antiviral therapy for at least 4 weeks and HBV viral load is undetectable prior to randomization
• Has had major surgery <3 weeks before the first dose of study treatment
• Is expected to require any other form of antineoplastic therapy while on study
• Has a history or current evidence of a gastrointestinal (GI) condition (e.g. inflammatory bowel disease, Crohn's disease, ulcerative colitis) or impaired liver function or diseases that in the opinion of the investigator may significantly alter the absorption or metabolism of oral medications
• Is getting chemotherapy and has clinically active diverticulitis, intra-abdominal abscess, GI obstruction, or peritoneal carcinomatosis
• Has preexisting neuropathy that is moderate in intensity
• Has received prior systemic cytotoxic chemotherapy or other targeted or biological antineoplastic therapy for metastatic disease
• Is unable or unwilling to take folic acid or vitamin B12 supplementation, for participants who will receive pemetrexed
• Has a known sensitivity to any component of carboplatin, paclitaxel, pemetrexed or any of their excipients
• Has received prior radiation therapy to the lung that is >30 Gray (Gy) within 6 months of the first dose of study treatment
• Has received a live vaccine within 30 days before the first dose of study treatment. Any licensed COVID-19 vaccine (including for Emergency Use) in a particular country is allowed as long as they are messenger ribonucleic acid (mRNA) vaccines, adenoviral vaccines, or inactivated vaccines. Investigational vaccines (ie, those not licensed or approved for Emergency Use) are not allowed
• Has received any prior immunotherapy and was discontinued from that treatment due to a severe or worse immune-related adverse event (irAE)
• Has had chemotherapy or biological cancer therapy within 4 weeks before the first dose of study treatment or has not recovered to Common Terminology Criteria for Adverse Events (CTCAE) Grade 1 or better from the AEs due to cancer therapeutics administered more than 4 weeks before the first dose of study treatment (including participants who had previous immunomodulatory therapy with residual irAEs)
• Is currently participating in or has participated in a study of an investigational agent or has used an investigational device within 4 weeks before the first dose of study treatment
• Previously had a severe hypersensitivity reaction to treatment with monoclonal antibodies (including pembrolizumab) and/or any of their excipients
• Has had an allogenic tissue/solid organ transplant