Inclusion Criteria  Has a diagnosis of multiple myeloma (MM) using current IMWG diagnostic criteria, and are relapsed or refractory to 1 to 3 prior lines of therapy*.  a. Has completed 3 or 4 cycles of a parenteral proteasome inhibitor (PI), and lenalidomide- or pomalidomide-based regimen and achieved a response of ≥ partial response (PR) with no evidence of disease progression as defined by IMWG criteria. This lead-in therapy to in-class transition (iCT) is not included as part of the 1 to 3 prior lines and should be completed no more than 28 days prior to initiation of IRd or IPd in this study.  Those with light chain myeloma and free light chain (FLC) only may be enrolled if they previously met or currently meet the criteria for a diagnosis of MM.  *A line of therapy is defined as one or more cycles of a planned treatment program. This may consist of one or more planned cycles of single-agent therapy or combination therapy, as well as a sequence of treatments administered in a planned manner. For example, a planned treatment approach of induction therapy followed by autologous stem-cell transplantation, followed by maintenance is considered one line of therapy. Autologous and allogenic transplants are permitted.  Has a diagnosis of non-secretory disease as long as the participant has a marker of disease that can be followed serially and assessed for response. Has an Eastern Cooperative Oncology Group (ECOG) performance status and/or other performance status of 0, 1, or 2 at the time of enrollment.  Exclusion criteria  Has Grade >2 peripheral neuropathy (PN), or Grade 2 PN with pain on clinical examination. Has not adequately recovered from other non-neuropathy AEs related to prior therapy in the opinion of the investigator at the time of enrollment. Is pomalidomide refractory. Has primary light chain amyloidosis (AL). Those with MM and concurrent AL are allowed. Has known central nervous system involvement by MM. Has infection requiring systemic antibiotic therapy or other serious infection within 14 days before enrollment. Has ongoing or active systemic infection, active hepatitis B or C virus infection, or known positive status for human immunodeficiency virus. Has been diagnosed or treated for another malignancy within 2 years before enrollment or has previously been diagnosed with another malignancy and has any evidence of residual disease. Participants with nonmelanoma skin cancer or carcinoma in situ of any type are not excluded if they have undergone complete resection. Has previously been treated with ixazomib or participated in a study with ixazomib whether treated with ixazomib or not.