Background: Histone deacetylase (HDAC) inhibitors (HDI) have a therapeutic niche in multiple myeloma (MM) due to their ability to salvage proteasome inhibitor and immunomodulatory drug responsiveness in refractory patients, thus raising interest in this therapeutic class. Selective HDI may further improve therapeutic efficacy. Methods: B cell lymphopoiesis was evaluated using Tg-HDAC11-eGFP mice expressing eGFP regulated by the HDAC11 promoter and congenic mouse strains deficient in HDAC11 expression globally (B6.HDAC11^-/-) or targeted to the B cell lineage (CD19Cre.HDAC11^-/-). Molecular and pharmacologic means were used to impair HDAC11 in established MM cell lines. Viability was measured by activated caspase-3, Annexin/PI (A/PI) staining, and CCK-8 viability assay. Subcellular localization changes induced by HDI and identification of the novel binding partner IRF4 were assessed by proximity ligation assay (PLA). Results: Profound eGFP increases in PC of Tg-HDAC11-eGFP mice suggest HDAC11 influences late stage B cell development. In addition, HDAC11 deficiency results in dramatically reduced PC in the bone marrow and periphery. PC depletion in CD19Cre.HDAC11^-/-mice suggests activity inherent in B cells rather than via externally derived signals. Quisinostat (QS), an HDI with enhanced HDAC11 selectivity, showed dose-dependent cytotoxicity in 10 MM cell lines (EC50 1-10nM). This activity was synergistic with bortezomib (BTZ) and carfilzomib (CFZ) in RPMI-8226 cells, while synergism was amplified in the BTZ-resistant RPMI-8226-B25 cell line. Exposure of RPMI-8226 cells to QS decreased detection of nuclear, but not cytosolic, HDAC11. Targeted siRNA–mediated silencing of HDAC11 in RPMI-8226 cells activated caspase-3 and reduced viability by A/PI staining. PLA of MM cell lines showed a novel interaction between HDAC11 and IRF4, an essential regulator of PC differentiation and MM survival, unmasking a potential mechanism for HDAC11-induced cytotoxicity in MM. This interaction was disrupted by QS. Conclusions: We show that HDAC11 inhibition reduces MM cell survival in vitro. Furthermore, we identify IRF4 as a binding partner for HDAC11 and propose this interaction as a candidate mechanism regulating PC maturation and MM survival.