• Participant must be \>18 years of age

• Monoclonal plasma cells in the bone marrow (BM) ≥10% or presence of a biopsy proven plasmacytoma and documented Multiple Myeloma (MM) satisfying at least one of the calcium, renal, anemia, bone (CRAB) criteria or biomarkers of malignancy criteria:

• CRAB criteria:

• i. Hypercalcemia: serum calcium \>0.25 mmol/L (\>1 mg/dL) higher than upper limit of normal (ULN) or \>2.75 mmol/L (\>11 mg/dL).

• ii. Renal insufficiency: creatinine clearance (CrCI) \<40mL/min or serum creatinine \>177 μmol/L (\>2 mg/dL).

• iii. Anemia: hemoglobin \>2 g/dL below the lower limit of normal or hemoglobin \<10 g/dL.

• iv. Bone lesions: one or more osteolytic lesions on skeletal radiography, Computed tomography (CT), or Positron emission tomography (PET-CT).

• Biomarkers of Malignancy:

‣ Clonal BM plasma cell percentage ≥60%.

‣ Involved: uninvolved serum free light chain (sFLC) ratio ≥100.

‣ More than 1 focal lesion on magnetic resonance imaging (MRI) studies.

• Must have at least ONE aspect of measurable disease, defined as one of the following:

‣ Urine M-protein excretion ≥200 mg/24 hrs (≥0.2 g/24 hrs), or

⁃ Serum M-protein concentration ≥0.5 g/dL (≥5.0 g/L), or

⁃ Serum FLC assay: involved FLC level ≥10 mg/dL (≥100 mg/L) and an abnormal serum FLC ratio (\<0.26 or \>1.65).

• Not a candidate for high-dose chemotherapy with autologous stem cell transplantation due to presence of significant comorbid condition(s), such as cardiac, pulmonary or other major organ dysfunction that are likely to have a negative impact on tolerability of high dose chemotherapy with stem cell transplantation. The patients will be assessed with the IMWG frailty index, a scoring system based on age, comorbidities, and cognitive and physical conditions, which is recommended by the European Society for Medical Oncology (ESMO) guidelines. Patients with International Myeloma Working Group (IMWG) frailty index score 1 or 2 will be considered transplant ineligible. The reason(s) for transplant ineligibility will be collected in the case report forms (CRFs).

• Eastern Cooperative Oncology Group Performance Status (ECOG PS) of 0-2.

• Adequate organ system function as defined by the below laboratory assessments. Hematologic

‣ Absolute neutrophil count (ANC) ≥1.25 X 10\^9/L; granulocyte colony-stimulating factor (G-CSF) use for the past 14 days is NOT allowed.

⁃ Hemoglobin ≥8.0 g/dL; transfusions are not permitted in the past 14 days prior to the assessment. Erythropoietin use is allowed.

⁃ Platelet count ≥50 x 10\^9/L if the BM is \>50% involved in myeloma. Otherwise, ≥75 x 10\^9/L; transfusions or platelet stimulating agents are NOT allowed in the past 14 days prior to the assessment.

• Hepatic

⁃ Total bilirubin ≤1.5xULN (isolated bilirubin ≥1.5xULN is acceptable if bilirubin is fractionated and direct bilirubin \<35%).

⁃ ALT ≤ 2.5xULN. Renal

⁃ Estimate glomerular filtration rate (eGFR) ≥30 mL/min/1.73 m2; calculated using the Modified Diet in Renal Disease (MDRD) formula.

⁃ Spot urine (albumin/creatinine ratio) \<500 mg/g (56 mg/mmol) OR

⁃ Urine Dipstick: Negative trace; if ≥1+ only eligible if confirmed \<500 mg/g \[56 mg/mmol\] by albumin/creatinine ratio (spot urine from first void).

• Female participants: contraceptive use 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 at least one of the following conditions applies:

⁃ Is not a woman of childbearing potential (WOCBP) defined as follows:

⁃ ≥ 45 years of age and has not had menses for \> 1 year

⁃ Patients who have been amenorrhoeic for \< 2 years without history of a hysterectomy and oophorectomy must have a follicle stimulating hormone value in the postmenopausal range upon screening evaluation

⁃ Post-hysterectomy, post-bilateral oophorectomy, or post-tubal ligation. Documented hysterectomy or oophorectomy must be confirmed with medical records of the actual procedure or confirmed by an ultrasound. Tubal ligation must be confirmed with medical records of the actual procedure.

• OR

⁃ Is a WOCBP and using two methods of reliable birth control (one method that is highly effective and one additional effective \[barrier\] method), beginning 4 weeks before initiating treatment with lenalidomide, during therapy, during dose interruptions and continuing for 4 weeks following discontinuation of lenalidomide treatment. WOCBP participants must use one method of reliable birth control that is highly effective for 4 months following discontinuation of belantamab mafodotin. WOCBP must also agree not to donate eggs (ova, oocytes) for the purpose of reproduction during treatment, during dose interruptions and for 28-days following the last dose of lenalidomide or 4 months following discontinuation of belantamab mafodotin treatment, whichever is longer.

• A WOCBP must have two negative pregnancy tests before therapy initiation. The first test should be performed within 10-14 days, and the second test within 24 hours before the start of lenalidomide therapy.

• The participant should not receive lenalidomide until the investigator has verified that the results of these pregnancy tests are negative. The investigator should evaluate the effectiveness of the contraceptive method in relation to the first dose of the study treatment. The investigator is responsible for a review of medical history, menstrual history, and recent sexual activity to decrease the risk for inclusion of a woman with a nearly undetected pregnancy.

• WOCBP is a female who:

⁃ has achieved menarche at some time point

⁃ has not undergone a hysterectomy or bilateral oophorectomy or

⁃ has not been naturally postmenopausal (amenorrhea following cancer therapy does not rule out childbearing potential) for at least 24 consecutive months (i.e., has had menses at any time in the preceding 24 consecutive months).

• Male participants: contraceptive use 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 during the intervention period and until 28 days after the last dose of lenalidomide or 6 months after the last dose of belantamab mafodotin, whichever is longer, to allow for clearance of any altered sperm.

⁃ Refrain from donating sperm

• PLUS either:

⁃ 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 contraception/barrier as detailed below:

• 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 woman of childbearing potential (including pregnant females).

• Participants must be able to understand the study procedures and agree to participate in the study by providing written informed consent.