Inclusion Criteria:

   - Be able to provide written, personally signed, and dated informed consent to
   participate in the study before completing any study-related procedures. As
   applicable, a parent/both parents or legally authorized representative (LAR) must
   provide signature of informed consent and there must be documentation of assent by the
   participants before completing any study-related procedures. During the COVID-19
   public health emergency, informed consent from a potential or current trial
   participant may, if permitted by local laws and regulations, be obtained via
   electronic informed consent (eIC) capabilities or an electronic face-to-face consent
   interview when these individuals are unable to travel to the site (FDA COVID-19
   Guidance, 27 January 2021, Q11).

   - Be greater than or equal to (>=) 16 years of age at the time of consent.

   - Be a recipient of hematopoietic stem cell transplant.

   - Have a documented asymptomatic CMV infection, with a screening value of CMV DNA >=1365
   International Units per millilitre (IU/mL) to less than or equal to (<=) 273000 IU/mL
   in whole blood or >=455 IU/mL to <=91000 IU/mL in plasma in 2 consecutive assessments,
   separated by at least 1 day, as determined by local or central specialty laboratory
   quantitative polymerase chain reaction (qPCR) or comparable quantitative CMV DNA
   results. Both samples should be taken within 14 days prior to randomization with
   second sample obtained within 5 days prior to randomization. Same laboratory and same
   sample type (whole blood or plasma) should be used for these assessments. Asymptomatic
   CMV infection is defined as an infection that does not present with tissue invasive
   CMV disease, as assessed by the investigator. Participants with CMV DNA less than (<)
   910 and >=455 IU/mL in plasma or <2730 and >=1365 IU/mL in whole blood will also need
   to meet at least 1 of the following criteria for high-risk CMV infection to be
   eligible:

      1. Human leukocyte antigen (HLA)-related (sibling) donor with at least 1 mismatch at
      1 of the following 3 HLA-gene loci: HLA-A, -B or -DR,

      2. Haploidentical donor

      3. Unrelated donor with at least 1 mismatch at 1 of the following 4 HLA -gene loci:
      HLA-A, -B, -C and -DRB1,

      4. Use of umbilical cord blood as stem cell source,

      5. Use of ex vivo T-cell-depleted grafts,

      6. Grade 2 or greater graft-versus-host-disease (GVHD), requiring the use of
      systemic corticosteroids (defined as the use of >=1 milligram per kilogram per
      day (mg/kg/day) of prednisone or equivalent dose of another corticosteroid).

   - Have the current CMV infection as the first episode of CMV viremia after HSCT, either
   primary or reactivation, which in the investigator's opinion requires treatment.

   - Per investigator's judgment, be eligible for treatment with valganciclovir.

   - Have all of the following results as part of screening laboratory assessments (results
   from either the central laboratory or a local laboratory can be used for
   qualification):

      1. Absolute neutrophil count to >=1000 per cubic millimeter (/mm^3) [1.0*10^9/L].

      2. Platelet count >=25,000/mm^3 [25*10^9/L].

      3. Hemoglobin >=8 grams per deciliter (g/dL).

      4. Estimated creatinine clearance >=30 milliliters per minute (mL/min).

   - Have a negative serum beta human chorionic gonadotropin (beta-HCG) pregnancy test at
   screening, if a female of child bearing potential. Urine pregnancy tests may be done
   per institutional requirements; however they are not sufficient for eligibility
   determination. Sexually active females of child bearing potential must agree to comply
   with any applicable contraceptive requirements of the protocol. If male, must agree to
   use an acceptable method of birth control, as defined in the protocol, during the
   study treatment administration period and for 90 days afterward the last dose of study
   treatment.

   - Be able to swallow tablets.

   - Have life expectancy of >=8 weeks.

   - Weigh >=40 kilograms (kg).

   - Be willing and have an understanding and ability to fully comply with study procedures
   and restrictions defined in the protocol.

Exclusion Criteria:

   - Have CMV tissue invasive disease as assessed by the investigator at the time of
   screening and randomization at Visit 2/Day 0.

   - Have a CMV infection that is known to be genotypically resistant to ganciclovir,
   valganciclovir, foscarnet, or cidofovir based on documented evidence.

   - Be presenting with recurrent CMV infection (defined as a new detection of CMV
   infection in a participants who had at least one previously documented episode of CMV
   infection post-transplant, and who has had at least 2 weeks of undetectable CMV DNA
   between the episodes during active surveillance, based on same local laboratory and
   same sample type). The Participants must also have been off any anti-CMV treatment
   between the current and prior infection. Otherwise, the current infection may be
   considered continuation of the prior infection.

   - Require ganciclovir, valganciclovir, foscarnet, or cidofovir administration for
   conditions other than CMV when study treatment is initiated (example: herpes simplex
   virus [HSV] co-infection requiring use of any of these agents after the randomization)
   or would need a co-administration with maribavir for CMV infection.

   - Be receiving leflunomide, letermovir, or artesunate when study treatment is initiated.

Note: Participants who may be receiving leflunomide must discontinue the use at least 14
days prior to randomization at Visit 2/Day 0 and the first dose of study treatment.
Participants receiving letermovir must discontinue use 3 days prior to first dose of study
treatment. Participants receiving artesunate must discontinue the use prior to the first
dose of study treatment.

   - Be on treatment with anti-CMV agents (ganciclovir, valganciclovir, foscarnet or
   letermovir) for the current CMV infection for longer than 72 hours.

   - Have known hypersensitivity to the active substance or to an excipient of the study
   treatments.

   - Have severe vomiting, diarrhea, or other severe gastrointestinal illness within 24
   hours prior to the first dose of study treatment that would preclude administration of
   oral medication.

   - Require mechanical ventilation or vasopressors for hemodynamic support at the time of
   randomization.

   - Be female and pregnant or nursing.

   - Have previously completed, discontinued, or have been withdrawn from this study.

   - Have received any investigational agent with known anti-CMV activity within 30 days
   before initiation of study treatment or CMV vaccine at any time.

   - Have received any unapproved agent or device within 30 days before initiation of study
   treatment.

   - Have any clinically significant medical or surgical condition that, in the
   investigator's opinion, could interfere with interpretation of study results,
   contraindicate the administration of the assigned study treatment, or compromise the
   safety or well-being of the participant.

   - Have previously received maribavir.

   - Have serum aspartate aminotransferase (AST) greater than (>) 5 times upper limit of
   normal (ULN) at screening, or serum alanine aminotransferase (ALT) >5 times ULN at
   screening, or total bilirubin >= 3.0*ULN at screening (except for documented Gilbert's
   syndrome), as analyzed by local or central laboratory.

   - Have known (previously documented) positive results for human immunodeficiency virus
   (HIV). Participants must have a confirmed negative HIV test result within 3 months of
   study entry or, if unavailable, be tested by a local laboratory during the screening
   period.

   - Have active malignancy with the exception of nonmelanoma skin cancer, as determined by
   the investigator. Participants who experience relapse or progression of their
   underlying malignancy (for which HSCT was performed), as determined by the
   investigator, are not to be enrolled.

   - Be undergoing treatment for acute or chronic hepatitis C