This study examines the combined influence of El Niño–Southern Oscillation (ENSO) and Madden–Julian Oscillation (MJO) characteristics on the interannual variability of the Indian Summer Monsoon Rainfall (ISMR), with a specific focus on La Niña years. Persistent equatorial Pacific cold tongue SST anomalies during the June to September (JJAS) season establish a favorable large-scale background for monsoon enhancement. However, ISMR exhibits substantial variability across La Niña years, ranging from excess to deficit rainfall, indicating that ENSO forcing alone is insufficient to explain monsoon outcomes. To address this, the role of intraseasonal variability associated with the MJO was investigated through phase frequency, persistence, and propagation characteristics during the June to September (JJAS) season. Results show that MJO phases 2–4 occur marginally more frequently than phases6–8, but phase persistence exhibits a stronger relationship with ISMR. Enhanced persistence in phases 2–4 is associated with excess rainfall, whereas prolonged residence in phases 6–7 shows a statistically significant negative correlation with ISMR. Year-wise analysis further demonstrates that monsoon deficits arise not only from the presence of suppressed phases but also from the absence of active phases. To further elucidate the mechanisms underlying these statistical relationships, composite analyses of contrasting monsoon conditions of wet and dry years were examined using detailed dynamical diagnostics. The analysis reveals a dynamically coherent and monsoon-supportive circulation structure during wet La Niña years, whereas during dry La Niña years it shows weakened ascent, eastward displacement of convective activity, and reduced dynamical support over the Indian region. In wet La Niña years, the MJO signal persisted in Phases 2–4, supporting moisture convergence over the Indian landmass, leading to higher rainfall. In dry La Niña years, the MJO signal persisted in Phases 6–7, favoring moisture divergence over the region and contributing to lower rainfall. These contrasts confirm that the seasonal realization of La Niña forcing depends critically on MJO phase persistence and associated large-scale circulation adjustments.