We examine a mechanism of how the frequency of the realization of the Madden–Julian oscillation (MJO) is influenced on the interannual time scale. The activity of MJO realization in each boreal winter is quantified by the number of MJO active days during the tracking of the Real-time multivariate MJO index. In active years of MJO realization (MJO-A), multiple MJO events are realized and they propagate into the western Pacific (WP) successfully, but this situation is not observed in inactive years (MJO-IA). This contrast is explained by whether vertical moisture advection over the WP is disrupted or not. It is related to differences in boreal-winter mean convection and circulations: MJO-A (MJO-IA) years are characterized by enhanced and suppressed (suppressed and enhanced) convection over the WP and Maritime Continent (MC), respectively. This modulation results from combined effects of the El Niño-Southern oscillation (ENSO) and quasi-biennial oscillation (QBO). During moderate El Niño, MJO is realized more actively as the Niño 3.4 index becomes higher irrespective of QBO, whereas during other ENSO phases, stronger QBO-easterly phases favor MJO realization irrespective of ENSO amplitudes. The connection between MJO realization and QBO except for El Niño conditions is due to zonally heterogeneous QBO impacts that the seasonal mean static stability change near the tropopause over the WP alters the mean convective activity there. This zonal heterogeneity and ENSO phase-dependency of QBO impacts is interpreted with a focus on vertical propagation of Kelvin wave structure over the MC, affected by both QBO winds and background Walker circulations.