Known as the Third Pole, the Tibetan Plateau (TP) has been recognized for its global influence on weather and climate, but research to harness the TP for improving subseasonal-to-interannual predictions has been lagging. Here using coupled climate simulations and hindcast experiments, we uncovered interannual predictability of the 2003 European summer heatwave that persisted from June to August with devastating impacts. Hindcasts initialized from the atmosphere, land, and ocean states of a coupled simulation that assimilates soil moisture and soil temperature over the TP from a land data product show substantial skill in predicting the 2003 European heatwave two years in advance. Hindcast sensitivity experiments using different combinations of atmosphere, land, and ocean states from the assimilation run and a free-running control simulation isolated the indispensable role of the spring TP snow cover anomalies in exciting the Rossby waves that contributed to the anomalous European summer temperature, with the remote impact of the TP on the Atlantic Ocean further playing a synergistic role in the extended predictability. These findings highlight the dominant and remote influence of the TP and motivate research on its role in providing subseasonal-to-interannual predictability of extreme events for regions worldwide.