Inclusion Criteria:

   - Must have been diagnosed with either Stage IIIA (> 1 mm tumor in lymph node)/B/C/D or
   Stage IV melanoma by American Joint Committee on Cancer (AJCC) v8 and have
   histologically confirmed melanoma that is completely surgically resected (free of
   disease) with negative margins in order to be eligible

   - Participants ≥ 18 years of age must have an Eastern Cooperative Oncology Group (ECOG)
   performance status of ≤ 1. Adolescent participants between 12 and < 18 years of age
   must have a Lansky/Karnofsky performance score ≥ 80%

   - Complete resection must be performed within 90 days prior to randomization

   - All participants must have disease-free status documented by a complete physical
   examination within 14 days prior to randomization and imaging studies within 35 days
   prior to randomization

   - Tumor tissue must be provided for biomarker analyses

Exclusion Criteria:

   - History of ocular melanoma

   - Untreated/unresected CNS metastases or leptomeningeal metastases

   - Active, known, or suspected autoimmune disease

   - Participants with serious or uncontrolled medical disorder

   - Prior immunotherapy treatment for any prior malignancy: No prior immunotherapies are
   permitted

   - Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection within 4 weeks
   prior to screening

   - History of myocarditis, regardless of etiology.

Other protocol-defined inclusion/exclusion criteria apply