Key Inclusion Criteria:

          1. Histologically confirmed diagnosis of HCC

          2. Barcelona Clinic Liver Cancer (BCLC) Stage B or C disease not amenable to or
             progressing after loco-regional therapy and not amenable to a curative treatment
             approach

          3. No prior systemic therapy for HCC (with the exception of HCC participants enrolled in
             the safety run-in substudy [Japan only])

          4. Measurable disease

          5. Child-Pugh score A

          6. Easter Cooperative Oncology Group (ECOG) Performance Status ≤ 1

          7. Adequate organ function

        Key Exclusion Criteria:

          1. Known fibrolamellar HCC, sarcomatoid HCC, or mixed cholangiocarcinoma and HCC
             histology

          2. Tumor thrombus involving main trunk of portal vein or inferior vena cava

          3. Loco-regional therapy to the liver within 28 days before randomization

          4. Clinical evidence of portal hypertension with bleeding esophageal or gastric varices
             at Screening, or within 6 months before randomization

          5. Bleeding or thrombotic disorder or any prescribed anticoagulant requiring therapeutic
             international normalized ratio monitoring (eg, warfarin or similar agents) at
             Screening, or within 6 months before randomization/enrollment

          6. Presence at Screening of active immune deficiency or autoimmune disease and/or prior
             history of any immune deficiency or autoimmune disease that may relapse

          7. Participant with any condition requiring systemic treatment with either
             corticosteroids (> 10 mg daily of prednisone or equivalent) or other immunosuppressive
             medication within 14 days before randomization

          8. History of interstitial lung disease or non-infectious pneumonitis, unless induced by
             radiation therapy

          9. QT interval corrected for heart rate (QTc) (corrected by Fridericia's method) > 450
             msec at Screening

        NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.