A Study of the Safety and Tolerability of ABBV-467 in Adult Participants With Relapsed/Refractory (R/R) Multiple Myeloma

* Documented diagnosis of multiple myeloma (MM). * Measurable disease defined as at least 1 of the following: * Serum monoclonal protein \>= 1g/dL. * Urine M-protein \>= 200mg/24 hours. * Serum immunoglobulin free light chain (FLC) \>= 10 mg/dL (100 mg/L), provided serum FLC ratio is abnormal. * Relapsed after or are refractory or intolerant to all established MM therapies that are both known to provide clinical benefit and locally available. * Received at least 3 prior lines of therapy including 1 or more immunomodulatory agents, 1 or more proteasome inhibitors, and 1 or more anti-CD38 monoclonal antibodies. * Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2. * Adequate hematologic, renal and hepatic function as described in the protocol. * Echocardiogram with ejection fraction \>= 50% and no other clinically significant findings that would increase the participant's susceptibility to cardiac toxicity.

* Prior exposure to any targeted myeloid cell leukemia-1 (MCL-1) inhibitor. * Antineoplastic therapy (including any cytotoxic, targeted and/or investigational therapy; but not including corticosteroids), within 28 days or 5 half-lives, whichever is shorter, prior to the first dose of study drug and through the last dose of study drug. * Autologous stem cell transplant within 90 days prior to start of study drug. * Allogenic stem cell transplant within 180 days prior to start of study drug. * History of acute or chronic pancreatitis. * Significant unresolved liver disease. * History of hepatitis B or human immunodeficiency virus (HIV) infection.