Inclusion Criteria: - ECOG performance status of 0-1. - Diagnosis of CLL or SLL that meets IWCLL 2008 criteria. - Active disease meeting at least 1 of the IWCLL 2008 criteria for requiring treatment. - Must have received at least one prior therapy for CLL/SLL. - Considered not appropriate for treatment or retreatment with purine analog based therapy. - Measurable nodal disease by CT. - Patients must be able to receive outpatient treatment and laboratory monitoring at the institution that administers study drug for the entire study. Exclusion Criteria: - Known CNS lymphoma or leukemia. - No documentation of cytogenetic and/or FISH in patient records prior to first dose of study drug. - Any history of Richter's transformation or prolymphocytic leukemia. - Uncontrolled Autoimmune Hemolytic Anemia (AIHA) or idiopathic thrombocytopenia purpura (ITP). - Prior exposure to ofatumumab or to ibrutinib. - Prior autologous/allogeneic transplant - History of prior malignancy, with the exception of certain skin cancers and malignancies treated with curative intent and with no evidence of active disease for more than 3 years. - Serologic status reflecting active hepatitis B or C infection. - Unable to swallow capsules or disease significantly affecting gastrointestinal function. - Uncontrolled active systemic fungal, bacterial, viral, or other infection. - History of stroke or intracranial hemorrhage within 6 months prior to the first dose of study drug. - Requires anticoagulation with warfarin.