Key Inclusion Criteria:

1. Histologically confirmed diagnosis of MCL
2. Prior systemic treatments for MCL (at least one line of anti-cluster of differentiate 20 (CD20) based immune or chemoimmunotherapy and at least one line of treatment with Bruton Tyrosine Kinase Inhibitor (BTKi) as mono- or combination therapy)
3. relapsed/refractory disease
4. Presence of measurable disease
5. Availability of archival tissue confirming diagnosis of MCL, or willing to undergo fresh tumor biopsy
6. Eastern Cooperative Oncology Group (ECOG) performance status of 0,1 or 2.
7. Adequate organ function

Key Exclusion Criteria:

1. Known central nervous system involvement by lymphoma
2. Prior malignancy other than MCL within the past 3 years, except for curatively treated basal or squamous cell skin cancer, superficial bladder cancer, carcinoma in situ of the cervix or breast, or localized Gleason score 6 prostate cancer.
3. Prior exposure to a Bcl-2 inhibitor (eg, venetoclax/ABT-199).
4. Prior autologous stem cell transplant within the last 3 months; or prior chimeric cell therapy within the last 3 months; or prior allogeneic stem cell transplant within the last 6 months or currently has an active graft-vs-host disease requiring the use of immunosuppressants.
5. Clinically significant cardiovascular disease.
6. Major surgery or significant injury ≤ 4 weeks prior to start of study treatment.
7. Active fungal, bacterial or viral infection requiring systemic treatment.

Note: Other protocol defined Inclusion/Exclusion criteria may apply.