A possibly important dynamical process for the Madden–Julian oscillation (MJO) convective initiation is proposed. An MJO event during the “CINDY2011” field campaign is triggered by eastward-moving lower-tropospheric mixed Rossby-gravity (MRG) wave packets, and its leading precursor is predominance of upper-tropospheric MRGs in the Indian Ocean (IO). Simple three-dimensional model experiments reveal that the upper-tropospheric MRGs in the IO are amplified particularly in the western IO (WIO) by their westward advection and wave accumulation due to the upper-level convergence in mean easterlies of the Walker circulation. The model also predicts downward dispersion of the amplified upper-tropospheric MRGs and resultant lower-tropospheric MRG wave packet formation. This MRG evolution consistently explains the MJO initiation process during CINDY2011, which is further verified by ray tracing for MRGs. Upper-tropospheric circumnavigating Kelvin waves assist the proposed mechanism by promoting MRG-wave accumulation (advection) in their westerly (easterly) phases via enhanced zonal convergence and weakened easterlies (enhanced easterlies).