Inclusion Criteria:  Participant must be ≥ 18 years at the time of screening. Documented TN CLL/SLL requiring treatment according to iwCLL guidelines 2018 (Hallek et al 2018).  Adequate BM function independent of growth factor or platelet transfusion support within 2 weeks of screening initiation as follows, unless cytopenia is due to CLL/SLL:  Absolute neutrophil count ≥ 1.0 × 10 9 /L. Platelet counts ≥ 30 × 10 9 /L; in cases of thrombocytopenia clearly due to CLL/SLL (per the discretion of the investigator), platelet count should be ≥ 10 × 10 9 /L.  Estimated CrCL > 30 mL/min calculated according to Cockcroft-Gault (using actual body weight) or directly measured with 24-hour urine collection,.  Males:  CrCL = Weight (kg) × (140 Age) (mL/min) 72 × serum creatinine (mg/dL)  Females:  CrCL = Weight (kg) × (140 Age) × 0.85 (mL/min) 72 × serum creatinine (mg/dL)  Adequate liver function, as indicated by a total bilirubin ≤ 1.5 × ULN, AST and ALT ≤ 3 × ULN value, unless directly attributable to the participant's CLL/SLL or to Gilbert's Syndrome (The ULN is based on institutional values). Eastern Cooperative Oncology Group Performance Status performance status 0 to 2 with no deterioration over the previous 2 weeks prior to baseline or day of first dosing. Ability to understand the purpose and risks of the study and provide signed and dated informed consent and authorization to use protected health information (in accordance with national and local patient privacy regulations). Willing and able to participate in all required evaluations and procedures in this study protocol including swallowing capsules and tablets without difficulty.  Exclusion Criteria:  As judged by the investigator, any evidence of past or current diseases that, in the investigator's opinion, makes it undesirable for the participant to participate in the study or that would jeopardize their safety or compliance with the protocol or would put the study at risk. Clinically significant cardiovascular disease, such as symptomatic arrhythmias, congestive heart failure, or myocardial infarction, within 6 months of screening or any Class 3 or 4 cardiac disease as defined by the New York Heart Association Functional Classification. Note: Participants with controlled, asymptomatic atrial fibrillation can enroll in the study. Active bleeding or history of bleeding diathesis (eg, hemophilia or von Willebrand disease). Uncontrolled autoimmune hemolytic anemia or idiopathic thrombocytopenic purpura. History of significant cerebrovascular disease/event, including stroke or intracranial hemorrhage, within 6 months before the first dose of study intervention. Child-Pugh B/C liver cirrhosis.  History of prior or current malignancy (including but not limited to known CNS lymphoma/leukemia or known prolymphocytic leukemia or history of, or currently suspected, Richter's syndrome) that could affect compliance with the protocol or interpretation of results. Exceptions can be made for the following based on physician discretion:  Curatively treated basal cell carcinoma or squamous cell carcinoma of the skin or carcinoma in situ of the cervix or carcinoma in situ of the prostate at any time prior to study. Other cancers not specified above that have been curatively treated by surgery and/or radiation therapy from which the participant is disease-free for ≥ 3 years without further treatment. An individual organ system dysfunction limiting the ability to receive the study intervention or any other life-threatening illness, medical condition, or organ system dysfunction that, in the investigator's opinion, could compromise the participants' safety or interfere with the absorption, distribution, metabolism, or excretion of the study interventions (eg, refractory nausea and vomiting, chronic gastrointestinal disease, inability to swallow the formulated product, previous significant bowel resection, or impaired resorption in the gastrointestinal tract). Known history of infection with HIV or any active significant infection (eg, bacterial, viral, or fungal; including participants with positive cytomegalovirus DNA PCR). History of or ongoing confirmed PML.  Serologic status reflecting active hepatitis B or C infection:  Participants who are anti-HBc positive and who are hepatitis B surface antigen (HBsAg) negative will need to have a negative PCR result before randomization and must be willing to undergo DNA PCR testing during the study. Those who are HbsAg-positive or hepatitis B PCR positive will be excluded. Participants who are hepatitis C antibody positive will need to have a negative PCR result before randomization. Those who are hepatitis C PCR positive will be excluded. Any prior CLL/SLL-specific therapies, except prior rituximab if used for autoimmune cytopenias and not as anti-CLL/SLL treatment. Corticosteroid use > 20 mg within 1 week before the first dose of study intervention, except as indicated for other medical conditions, such as autoimmune cytopenias, inhaled steroid for asthma, topical steroid use, or as premedication for administration of study intervention or contrast. Participants requiring steroids at daily doses > 20 mg prednisone equivalent systemic exposure daily, or those who are administered steroids for leukemia control or white blood cell count lowering, are excluded. Of note, patients may receive corticosteroids as doses > 20 mg as per institutional standards for obinutuzumab pre-medication prior to C1D1. Prior radio- or toxin-conjugated antibody therapy. Prior allogeneic stem cell or autologous transplant. Known history of hypersensitivity or anaphylaxis to study intervention(s), including active product or excipient components. Requires treatment with a strong cytochrome CYP3A4 inhibitor/inducer. The use of strong CYP3A inhibitors within 1 week or strong CYP3A inducers within 3 weeks of the first dose of study drug is prohibited. Requires or receiving anticoagulation with warfarin or equivalent vitamin K antagonists (other anticoagulants allowed). Requires treatment with proton pump inhibitors (eg, omeprazole, esomeprazole, lansoprazole, dexlansoprazole, rabeprazole, or pantoprazole). Note: Participants receiving proton pump inhibitors who switch to H2-receptor antagonists or antacids are eligible for enrollment to this study. Vaccination with live vaccines 28 days prior to registration for study screening. Major surgical procedure within 28 days of first dose of study intervention. Note: If a participant had major surgery, they must have recovered adequately from any toxicity and/or complications from the intervention before the first dose of study intervention. Concurrent participation in another therapeutic clinical trial. Use of investigational agents that interfere with the study intervention(s) within 28 days or 5 half-lives (whichever is shorter) prior to registration for study screening. Prothrombin time (PT)/INR or activated partial thromboplastin time, in the absence of lupus anticoagulant, > 2 × ULN. Currently pregnant (confirmed with positive pregnancy test) or breast feeding. Women of Childbearing Potential (WOCBP) a negative pregnancy test is required for all WOCBP within 21 days before start of study intervention, followed by immediate highly effective contraception; further pregnancy testing will be performed monthly). Fertile men or WOCBP unless the following criteria are met: Willing to use 2 methods of reliable contraception, including one highly effective contraceptive method (Pearl Index < 1) and one additional effective (barrier) method during study intervention and for 2 days after last acalabrutinib dose (for WOCBP), 30 days after last venetoclax dose (fertile men and WOCBP), and 6 months after last obinutuzumab dose for fertile men and 18 months after last obinutuzumab dose for WOCBP.