Inclusion Criteria:
* Capable of giving signed informed consent.
* Male or female, 18 years or older.
* Have a confirmed diagnosis of multiple myeloma (MM) as defined by the International Myeloma Working Group (IMWG) criteria.
* Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2.
* Have been previously treated with at least 1 prior line of MM therapy including a lenalidomide-containing regimen and must have documented disease progression during or after their most recent therapy. (Participants treated with lenalidomide ≥10 mg daily for at least 2 consecutive cycles are eligible).
* Must have at least 1 aspect of measurable disease defined as one of the following;
1. Urine M-protein excretion greater than or equal to (≥)200 milligrams (mg) per 24-hour, or
2. Serum M-protein concentration ≥0.5 grams/deciliters (g/dL) (≥5.0 g/liter \[L\]), or
3. Serum free light chain (FLC) assay: involved FLC level ≥10 mg/dL (≥100 mg/L) and an abnormal serum free light chain ratio (less than \[\<\]0.26 or greater than \[\>\]1.65) only if participant has no measurable urine or serum M spike.
* Have undergone autologous stem cell transplant (ASCT) or are considered transplant ineligible. Participants with a history of ASCT are eligible for study participation provided the following eligibility criteria are met: a. ASCT was \>100 days prior to the first dose of study medication. b. No active bacterial, viral, or fungal infection(s) present
* All prior treatment-related toxicities (defined by National Cancer Institute Common Terminology Criteria for Adverse Events \[NCI-CTCAE\] version 5.0) must be less than or equal to (≤)Grade 1 at the time of enrolment, except for alopecia.
* Adequate organ system functions as mentioned in the protocol.
* Male and female participants agree to abide by protocol-defined contraceptive requirements.
* In Japan, Hepatitis B participants who are hepatitis B surface antigen (HbsAg)- (e.g. HBsAb+/HbsAg-, HBcAb+/HbsAg-, HBcAb+/HBsAb+/HbsAg-) are eligible for inclusion in this study if hepatitis B virus (HBV) DNA is undetectable. A patient with HBsAg+ is eligible if HBV DNA is undetectable after assessing hepatitis B e antigen (HBeAg), hepatitis B e antibody (HBeAb) and HBV DNA, and if a hepatologist agrees with the participation into this study.
Exclusion Criteria:
* Active plasma cell leukemia, symptomatic amyloidosis or active polyneuropathy, organomegaly, endocrinopathy, monoclonal plasma proliferative disorder, and skin changes (POEMS) syndrome at the time of screening.
* Prior allogeneic SCT.
* Systemic anti-myeloma therapy (including chemotherapy and systemic steroids) within 14 days or five half-lives (whichever is shorter) preceding the first dose of study drug; prior treatment with a monoclonal antibody drug within 30 days of receiving the first dose of study drugs.
* Plasmapheresis within 7 days prior to the first dose of study drug.
* Received prior treatment with or intolerant to pomalidomide.
* Received prior Beta cell maturation antigen (BCMA) targeted therapy.
* Intolerant to bortezomib or refractory to bortezomib (for example; participant experienced progressive disease during treatment, or within 60 days of completing treatment, with a bortezomib-containing regimen of 1.3 mg/meter square \[m\^2\] twice weekly).
* Evidence of cardiovascular risk including any of the following;
1. Evidence of current clinically significant untreated arrhythmias, including clinically significant electrocardiogram abnormalities including second degree (Mobitz type II) or third degree atrioventricular (AV) block.
2. Recent history within (3 months of screening) of myocardial infarction, acute coronary syndromes (including unstable angina), coronary angioplasty, or stenting or bypass grafting .
3. Class III or IV heart failure as defined by the New York Heart Association (NYHA) functional classification system
4. Uncontrolled hypertension.
* Any major surgery within the last 4 weeks.
* Previous or concurrent invasive malignancy other than multiple myeloma, except:
1. The disease must be considered medically stable for at least 2 years; or
2. The participant must not be receiving active therapy, other than hormonal therapy for this disease.
* Known immediate or delayed hypersensitivity reaction or idiosyncratic reaction to belantamab mafodotin or drugs chemically related to belantamab mafodotin, or any of the components of the study treatment.
* Evidence of active mucosal or internal bleeding.
* Cirrhosis or current unstable liver or biliary disease per investigator assessment defined by the presence of ascites, encephalopathy, coagulopathy, hypoalbuminemia, esophageal or gastric varices, persistent jaundice.
* Active infection requiring treatment.
* Known or active human immunodeficiency virus (HIV) infection, hepatitis B or hepatitis C will be excluded unless the protocol-defined criteria are met.
* Presence of active renal conditions (such as infection, severe renal impairment requiring dialysis or any other condition that could affect participant's safety).
* Ongoing Grade 2 peripheral neuropathy with pain within 14 days prior to randomization or ≥Grade 3 peripheral neuropathy.
* Active or history of venous and arterial thromboembolism within the past 3 months.
* Contraindications to or unwilling to undergo protocol-required anti-thrombotic prophylaxis.
* Current corneal disease except for mild punctate keratopathy.
* Any serious and/or unstable pre-existing medical, psychiatric disorder or other conditions (including laboratory abnormalities) that could interfere with participant's safety, obtaining informed consent or compliance to the study procedures.
* Pregnant or lactating female.
