Inclusion Criteria:

          -  Participants are capable of giving signed informed consent which includes compliance
             with the requirements and restrictions listed in the Informed Consent Form.

          -  Male and/or female must be 18 years of age or older, at the time of signing the
             informed consent.

          -  Eastern Cooperative Oncology Group performance status 0-2.

          -  Participants with histologically or cytologically confirmed diagnosis of multiple
             myeloma, as defined in International Myeloma Working Group criteria: 1. Has undergone
             autologous stem cell transplant (SCT) or is considered transplant-ineligible; 2. Has
             failed at least 2 prior lines of anti-myeloma treatments, including an
             immunomodulatory drugs (example [e.g.], lenalidomide or pomalidomide) and a proteasome
             inhibitor (e.g., bortezomib, ixazomib or carfilzomib).

          -  Participants has measurable disease with at least one of the following: Serum
             M-protein >=0.5 grams per deciliter (g/dL) (>=5 grams per liter [g/L]); Urine
             M-protein >=200 milligram per 24 hours (mg/24 hr); and Serum free light chain assay:
             Involved free light chain level >=10 milligrams per deciliter (mg/dL) (>=100
             milligrams per liter [mg/L]) and an abnormal serum free light chain ratio (<0.26 or
             >1.65).

          -  Participants with a history of autologous SCT are eligible for study participation
             provided the following eligibility criteria are met: 1. Transplant was >100 days prior
             to study enrollment, 2. No active infection(s), and 3. Participant meets the remainder
             of the eligibility criteria outlined in this protocol.

          -  Participants with adequate organ system functions as defined follows: Absolute
             neutrophil count >=1.0 x 10^9/liter (L); Hemoglobin >=8.0 g/dL (or 4.9 millimoles per
             liter); Platelets >= 75 x 10^9/L; Serum bilirubin and aspartate aminotransferase:
             Group 1 (normal) serum bilirubin and aspartate aminotransferase <=upper limit of
             normal (ULN); Group 2 (moderate) serum bilirubin >1.5-3 x ULN and any aspartate
             aminotransferase; alanine aminotransferase <=5 x ULN; Estimated glomerular filtration
             rate >=30 milliliter per minute per 1.73 meter square (mL/min/m^2); and left
             ventricular ejection fraction by echocardiograms >=45%.

          -  Main additional inclusion criteria in Group 1 (matched control participants): Matched
             to at least one moderate hepatic impaired participant by Baseline albumin levels
             (+/-10%) and Baseline weight (+/-20%).

          -  Female participants: Contraceptive use by women should be consistent with local
             regulations regarding the methods of contraception for those participating in clinical
             studies. A female participant is eligible to participate if she is not pregnant or
             breastfeeding, and not a woman of childbearing potential (WOCBP) or is a WOCBP and
             using a contraceptive method that is highly effective (with a failure rate of <1% per
             year), preferably with low user dependency, during the intervention period and for at
             least 9 months after the last dose of study intervention and agrees not to donate eggs
             (ova, oocytes) for the purpose of reproduction during this period. The investigator
             should evaluate the effectiveness of the contraceptive method in relationship to the
             first dose of study intervention. A WOCBP must have a negative highly sensitive serum
             pregnancy test within 72 hours of dosing on Cycle 1 Day 1 and agree to use effective
             contraception during the study and for 9 months after the last dose of study
             medication. The investigator is responsible for review of medical history, menstrual
             history, and recent sexual activity to decrease the risk for inclusion of a woman with
             an early undetected pregnancy.

          -  Male participants: Contraceptive use by men should be consistent with local
             regulations regarding the methods of contraception for those participating in clinical
             studies. Male participants are eligible to participate if they agree to the following
             from the time of first dose of study until 6 months after the last dose of study
             treatment to allow for clearance of any altered sperm, Plus, any of the following: Be
             abstinent from heterosexual intercourse as their preferred and usual lifestyle
             (abstinent on a long term and persistent basis) and agree to remain abstinent; or must
             agree to use a male condom even if they have undergone a successful vasectomy and
             female partner to use an additional highly effective contraceptive method with a
             failure rate of <1% per year as when having sexual intercourse with a WOCBP (including
             pregnant females).

          -  Participants with a history of Hepatitis B virus and/or Hepatitis C virus exposure are
             eligible under specific conditions.

        Exclusion Criteria:

          -  Active plasma cell leukemia at the time of screening. Symptomatic amyloidosis, active
             polyneuropathy, organomegaly, endocrinopathy, myeloma protein and skin changes,
             Waldenstroem Macroglobulinemia.

          -  Participants had a prior allogeneic SCT.

          -  Participant has received an investigational drug within 14 days or 5 half-lives,
             whichever is shorter, preceding the first dose of study drug. This includes prior
             treatment with a monoclonal antibody or prior belantamab mafodotin. The only exception
             is emergency use of a short course of systemic corticosteroids (equivalent of
             dexamethasone 40 milligrams per day [mg/day] for a maximum of 4 days) before
             treatment.

          -  Participant has received a strong Organic-anion transporting polypeptide (OATP)
             inhibitor within 14 days or 5 half-lives, whichever is shorter, preceding the first
             dose of study drug.

          -  Systemic active infection requiring treatment.

          -  Any unresolved toxicity >=Grade 2 from previous treatment except for alopecia, or
             peripheral neuropathy up to Grade 2.

          -  Plasmapheresis within 7 days prior to the first dose of study drug. Screening
             laboratory values must be performed after last plasmapheresis.

          -  Any major surgery within the last 4 weeks.

          -  Any serious and/or unstable pre-existing medical, psychiatric disorder or other
             conditions (including lab abnormalities except hepatic impairment) that could
             interfere with participant's safety, obtaining informed consent or compliance to the
             study procedures.

          -  Evidence of active mucosal or internal bleeding.

          -  Current unstable liver or biliary disease per investigator assessment defined by the
             sudden onset of, or clinically relevant changes in: ascites, encephalopathy,
             coagulopathy, hypoalbuminemia, esophageal or gastric varices, persistent jaundice, in
             the last 14 days prior to the first dose. Participants with cirrhosis are excluded.
             Participants with focal lesions due to other causes than underlying multiple myeloma
             are excluded.

          -  Participants with acute hepatitis B virus infection are excluded. Participants with
             chronic hepatitis B infection (active or core antibody positive) are only allowed if
             the criteria from Organ System Function are fulfilled and if appropriate antiviral
             treatment per local guidance (e.g. tenofovir or entecavir) is started before starting
             belantamab mafodotin, continues through to completion of belantamab mafodotin therapy
             and is not to be stopped unless advised by local hepatology or virology.

          -  Participants with evidence of hepatitis C virus infection, defined as positive
             hepatitis C virus - ribonucleic acid test result at screening or within 3 months prior
             to first dose of study treatment, are excluded unless successfully treated prior to
             enrollment with a curative 8-12 week antiviral treatment course and the hepatitis C
             virus - ribonucleic acid negative status has been confirmed after at least 4 weeks
             washout of the antiviral treatment.

          -  Participants with Gilbert's syndrome.

          -  Participants with previous or concurrent malignancies other than multiple myeloma,
             except: The disease must be considered medically stable for at least 2 years; or the
             participant must not be receiving active therapy, other than hormonal therapy for this
             disease.

          -  Evidence of cardiovascular risk including any of the following: Evidence of current
             clinically significant untreated arrhythmias, including clinically significant
             electrocardiogram abnormalities including second degree (Mobitz Type II) or third
             degree atrioventricular block; History of myocardial infarction, acute coronary
             syndromes (including unstable angina), coronary angioplasty, or stenting or bypass
             grafting within 3 months of Screening; Class III or IV heart failure as defined by the
             New York Heart Association functional classification system; History of severe
             non-ischemic cardiomyopathy; and Uncontrolled hypertension.

          -  Known immediate or delayed hypersensitivity reaction or idiosyncratic reaction to
             drugs chemically related to belantamab mafodotin, or any of the components of the
             study treatment.

          -  Known human immunodeficiency virus infection.

          -  Current corneal epithelial disease except for mild punctuate keratopathy.

          -  Participant is a woman who is pregnant or breastfeeding.