Marine heatwaves (MHWs) along the tropical southeast Atlantic (TSEA) coast have devastating impacts on marine ecosystems and productivity. Through observational analysis and numerical model experiments, we demonstrate that positive Indian Ocean Dipole (pIOD) can intensify TSEA coastal MHWs during austral summer through two distinct processes. First, pIOD induces westerly wind anomalies over the equatorial Atlantic, causing thermocline deepening along the TSEA coast through oceanic Kelvin waves, favoring development of MHWs. Second, pIOD enhances rainfall over central Africa, increasing Congo River discharge and resulting in a shallower mixed layer in the TSEA coastal region, also promoting MHW formation. We further develop an empirical model using pIOD as the predictor for TSEA MHWs, demonstrating high predictive skill with a three-month lead time. In a warming climate, the remote influence of pIOD on TSEA MHWs may be further exacerbated, underscoring critical need to incorporate this factor into marine hazard forecasting for the region.