Inclusion Criteria:
* Participant must be greater than or equal to 18 years of age.
* Participant must have diagnosis of chronic lymphocytic leukemia (CLL) that meets published 2008 Modified IWCLL NCI-WG (International Workshop for Chronic Lymphocytic Leukemia National Cancer Institute-Working Group) Guidelines.
* Participant has an indication for treatment according to the 2008 Modified IWCLL NCI WG Guidelines;
* Participant has clinically measurable disease (lymphocytosis \> 5 × 10\^9/L and/or palpable and measurable nodes by physical exam and/or organomegaly assessed by physical exam);
* Participant must be refractory or have relapsed after receiving at least one prior line of therapy (participants that have progressed after 1 cycle of treatment or have completed at least 2 cycles of treatment for a given line of therapy) or previously untreated CLL (previously untreated CLL participants must have received no prior chemotherapy or immunotherapy. Participants with a history of emergency, loco-regional radiotherapy (e.g., for relief of compressive signs or symptoms) are eligible. In addition, participants must meet the CLL diagnostic criteria above and must have \> 5 × 10\^9/L B-Lymphocytes in the peripheral blood.);
* Participants must have 17p deletion, assessed by local laboratory (in bone marrow or peripheral blood) or assessed by central laboratory (peripheral blood).
* Participant has an Eastern Cooperative Oncology Group (ECOG) performance score of less than or equal to 2.
* Participant must have adequate bone marrow function at Screening as follows:
* Absolute Neutrophil Count (ANC) greater than or equal to 1000/µL, or
* For subjects with an ANC less than 1000/µL at Screening and bone marrow heavily infiltrated with underlying disease (unless cytopenia is clearly due to marrow involvement of CLL), growth factor support may be administered after Screening and prior to the first dose of ABT-199 to achieve the ANC eligibility criteria (greater than or equal to 1000/µL);
* Platelets greater than 30,000/mm\^3 (without transfusion support within 14 days of Screening, without evidence of mucosal bleeding, without known history of bleeding episode within 3 months of Screening, and without history of bleeding disorder);
* Hemoglobin greater than or equal to 8.0 g/dL.
* Participant must have adequate coagulation, renal, and hepatic function, per laboratory reference range at Screening as follows:
* Activated partial thromboplastin time (aPTT) and prothrombin time (PT) not to exceed 1.5 × the upper limit of normal;
* Calculated creatinine clearance greater than 50 mL/min using 24-hour Creatinine Clearance or modified Cockcroft-Gault equation (using Ideal Body Mass \[IBM\] instead of Mass). For participants that have body mass index (BMI) of \> 30 kg/m\^2 or \< 19 kg/m\^2, 24-hour measured urine creatinine clearance is required;
* Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) less than or equal to 3.0 × the upper normal limit of institution's normal range; Bilirubin less than or equal to 1.5 × upper limit of normal. Participants with Gilbert's Syndrome may have a bilirubin greater 1.5 × upper limit of normal, per correspondence between the investigator and AbbVie medical monitor.
* For participants at high risk of tumor lysis syndrome a pre-approval by the AbbVie medical monitor is required prior to enrollment.
Exclusion Criteria:
* Participant has undergone an allogeneic stem cell transplant.
* Participant has developed Richter's transformation confirmed by biopsy.
* Participant has prolymphocytic leukemia.
* Participant has active and uncontrolled autoimmune cytopenias (for 2 weeks prior to Screening), including autoimmune hemolytic anemia and idiopathic thrombocytopenic purpura despite low dose corticosteroids.
* Participant has previously received ABT-199.
* Participant has received a biologic agent for anti-neoplastic intent within 30 days prior to the first dose of study drug.
* Participant has received any of the following within 14 days or 5 half-lives as applicable prior to the first dose of study drug, or has not recovered to less than Common Toxicity Criteria (CTC) grade 2 clinically significant adverse effect(s)/toxicity(s) of the previous therapy:
* Any anti-cancer therapy including chemotherapy, or radiotherapy;
* Investigational therapy, including targeted small molecule agents.
* Participant has known allergy to both xanthine oxidase inhibitors and rasburicase.
