Inclusion Criteria:

          1. Have a histologically or cytologically confirmed diagnosis nonsquamous NSCLC.

          2. Have stage IV nonsquamous NSCLC.

          3. Have confirmation that epidermal growth factor receptor (EGFR), anaplastic lymphoma
             kinase (ALK), or Proto-oncogene tyrosine-protein kinase (ROS1)-directed therapy is not
             indicated.

          4. Have measurable disease based on RECIST 1.1.

          5. Have provided archival tumor tissue sample or newly obtained core or incisional biopsy
             of a tumor lesion not previously irradiated.

             Note: Adequacy of biopsy specimen for the above analyses must be confirmed by the
             central laboratory before the participant can start the induction phase. Submission of
             another tumor specimen may be required prior to enrolling the participant, if adequate
             tumor tissue was not provided the first time.

          6. Have a life expectancy of at least 3 months.

          7. Have a performance status of 0 or 1 on the Eastern Cooperative Oncology Group (ECOG)
             Performance Status assessed within 7 days prior to the administration of study
             intervention.

          8. Have not received prior systemic treatment for their advanced/metastatic NSCLC.

          9. Have adequate organ function.

         10. Male and female participants who are not pregnant and of childbearing potential must
             follow contraceptive guidance during the treatment period and for 180 days afterwards.

         11. Male participants must refrain from donating sperm, and female participants must
             refrain from donating eggs to others or freeze/store for her own use during the
             treatment period and for 180 days afterwards.

        Exclusion Criteria:

          1. Has predominantly squamous cell histology NSCLC.

          2. Has a known additional malignancy that is progressing or has progressed within the
             past 3 years requiring active treatment.

          3. Has known active central nervous system (CNS) metastases and/or carcinomatous
             meningitis.

          4. Has a severe hypersensitivity (≥Grade 3) to pembrolizumab and/or any of its
             excipients.

          5. Has a known hypersensitivity to any components or excipients of cisplatin,
             carboplatin, pemetrexed, or olaparib.

          6. Has an active autoimmune disease that has required systemic treatment in past 2 years.

          7. Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy.

          8. Has a known history of human immunodeficiency virus (HIV) infection, a known history
             of hepatitis B infection, or known active hepatitis C virus infection.

          9. Has interstitial lung disease, or history of pneumonitis requiring systemic steroids
             for treatment.

         10. Has received prior therapy with olaparib or with any other polyadenosine 5'
             diphosphoribose (polyADP ribose) polymerization (PARP) inhibitor.

         11. Has received prior therapy with an agent directed to programmed cell death ligand 1
             (PD-L1), anti PD-L2, or directed to a stimulatory or co-inhibitory T-cell receptor
             (e.g., cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), OX-40, CD137).

         12. Has myelodysplastic syndrome (MDS)/acute myeloid leukemia (AML) or with features
             suggestive of MDS/AML.

         13. Has not completed palliative radiotherapy within 7 days of the first dose.
             Participants must have recovered from all radiation-related toxicities and not require
             corticosteroids.