Inclusion Criteria:
1. Histological or cytological confirmation of relapsed or refractory acute myelogenous leukemia (AML) (by World Health Organization \[WHO\] classification) or untreated AML in participants who are unfit for intensive therapy.
2. Participant has an Eastern Cooperative Oncology Group (ECOG) Performance score of 0 to 2.
3. Participant must have adequate renal function as demonstrated by a calculated creatinine clearance ≥ 50 mL/min; determined via urine collection for 24-hour creatinine clearance or by the Cockcroft Gault formula using ideal body mass (IBM) instead of mass.
4. Participant must have adequate liver function as demonstrated by:
* aspartate aminotransferase (AST) ≤ 3.0 × upper limit of normal (ULN)\*
* alanine aminotransferase (ALT) ≤ 3.0 × ULN\*
* bilirubin ≤ 1.5 × ULN\* \*unless considered due to leukemic organ involvement. (Participants with Gilbert's Syndrome may have had a bilirubin \> 1.5 × ULN per discussion between the investigator and AbbVie medical monitor)
Exclusion Criteria:
1. Participant has received acute anti-cancer therapy including chemotherapy, immunotherapy, radiotherapy, hormonal or any investigational therapy within 14 days or 5 half-lives (whichever is shorter) prior to first dose of ABT-199.
2. Participant has received a monoclonal antibody for anti-neoplastic intent within 8 weeks prior to the first dose of study drug.
3. Participant has received potent Cytochrome P450, family 3, subfamily A (CYP3A) inducers (such as rifampin, carbamazepine, phenytoin and St. John's wort) and warfarin or requires the use of warfarin (due to potential drug-drug interactions that may potentially increase the exposure of warfarin and complications of this effect) within 7 days prior to the first dose of study drug.
4. Participant has received CYP3A inhibitors (such as fluconazole, ketoconazole, and clarithromycin) within 5 days prior to the first dose of study drug.
5. Participant has a white blood cell count \> 25 x 10\^9/L.
6. Participant has acute promyelocytic leukemia (French-American-British Class M3 AML).
7. Participants with known active central nervous system (CNS) disease.
