Inclusion Criteria:

1. Confirmed diagnosis of CLL/SLL requiring therapy, per iwCLL 2018 criteria
2. Eastern Cooperative Oncology Group (ECOG) Performance Status 0-2
3. Adequate organ function
4. Platelets greater than or equal to (≥)75 x 10⁹/liter (L) (≥50 × 10⁹/L for patients with evidence of bone marrow infiltrate), hemoglobin ≥8 grams/deciliter (g/dL), and absolute neutrophil count ≥0.75 x 10⁹/L
5. Kidney function: Estimated creatinine clearance ≥40 milliliters per minute (mL/min)

Exclusion Criteria:

1. Known or suspected Richter's transformation at any time preceding enrollment
2. Prior systemic therapy for CLL/SLL
3. Presence of 17p deletion
4. Central nervous system (CNS) involvement
5. Active uncontrolled auto-immune cytopenia (e.g., autoimmune hemolytic anemia [AIHA], idiopathic thrombocytopenic purpura [ITP])
6. Significant cardiovascular disease
7. Active hepatitis B or hepatitis C
8. Active cytomegalovirus (CMV) infection
9. Active uncontrolled systemic bacterial, viral, fungal, or parasitic infection
10. Known human immunodeficiency virus (HIV) infection, regardless of cluster of differentiation 4 (CD4) count
11. Concurrent use of investigational agent or anticancer therapy except hormonal therapy
12. Patients requiring therapeutic anticoagulation with warfarin or another Vitamin K antagonist
13. Vaccination with a live vaccine within 28 days prior to randomization

Patients with the following hypersensitivity:

1. Known hypersensitivity, including anaphylaxis, to any component or excipient of pirtobrutinib or bendamustine
2. Prior significant hypersensitivity to rituximab