The following criteria is provided for health care professionals.

Inclusion Criteria:

* Confirmed diagnosis of CLL/SLL requiring therapy per iwCLL 2018 criteria
* Previous treatment with at least one line of therapy that may include a covalent Bruton's tyrosine kinase (BTK) inhibitor
* Platelets greater than or equal to (≥)50 x 10⁹/liter (L), hemoglobin ≥8 grams/deciliter (g/dL) and absolute neutrophil count ≥1.0 x 10⁹/L
* Adequate organ function
* Eastern Cooperative Oncology Group (ECOG) Performance Status 0-2
* Estimated creatinine clearance ≥30 milliliters per minute (mL/min)

Exclusion Criteria:

* Known or suspected Richter's transformation at any time preceding enrollment
* Prior therapy with a non-covalent (reversible) BTK inhibitor
* Patients requiring therapeutic anticoagulation with warfarin or another Vitamin K antagonist
* Current treatment with strong cytochrome P450 (CYP) 3A4 (CYP3A4) inhibitors or inducers
* Prior therapy with venetoclax
* Central nervous system (CNS) involvement
* Active uncontrolled systemic bacterial, viral, fungal, or parasitic infection
* Known human immunodeficiency virus (HIV) infection, regardless of cluster of differentiation 4 (CD4) count
* Allogeneic stem cell transplantation (SCT) or chimeric antigen receptor (CAR)-T within 60 days
* Active hepatitis B or hepatitis C
* Known active cytomegalovirus (CMV) infection
* Uncontrolled immune thrombocytopenic purpura (ITP) or autoimmune hemolytic anemia (AIHA)
* Significant cardiovascular disease
* Vaccination with a live vaccine within 28 days prior to randomization
* Patients with the following hypersensitivity:

* Known hypersensitivity to any component or excipient of pirtobrutinib and venetoclax
* Prior significant hypersensitivity to rituximab
* Known allergy to allopurinol and inability to take uric acid lowering agent