The primary purpose of this study is to evaluate the efficacy of ublituximab in adult participants with MG responding to treatment with efgartigimod.

Inclusion Criteria:

1. Documentation of MG diagnosis.
2. Eligible for treatment with efgartigimod per effective local product label, confirmed by serological testing at screening.
3. MG-ADL score at the time of screening more than or equal to (≥) 6 and less than or equal to (≤) 10 with more than (>) 50 percent (%) of this score attributed to non-ocular items, or an MG-ADL score ≥ 11.

Exclusion Criteria:

1. Active chronic (or stable but treated with immune therapy) disease of the immune system other than MG (e.g., rheumatoid arthritis, scleroderma, Sjögren's syndrome, Crohn's disease, ulcerative colitis, etc.) or immunodeficiency syndrome (hereditary immune deficiency, drug-induced immune deficiency, etc.).
2. Lack of efficacy or observed safety concerns from prior neonatal Fc receptor (FcRn) treatment.
3. Prior treatment with B-cell depleting therapy, alemtuzumab, total lymphoid irradiation, bone marrow transplant, T-cell vaccination therapy, or natalizumab at any time prior to screening.
4. Participants with significantly impaired organ function.
5. History of life-threatening injection/infusion related reaction (IRR/ISR), hypersensitivity, or anaphylactic reaction with components of efgartigimod or ublituximab solutions, protocol-allowed rescue medications, or protocol required pre-treatment medications.
6. Unwillingness or inability to comply with study and/or follow-up procedures outlined in the protocol.

Note: Other protocol-specified Inclusion/Exclusion criteria may apply.