We apply a novel computational approach to assess, for the first time, volcanic ash dispersal during the Campanian Ignimbrite (Italy) super‐eruption providing insights into eruption dynamics and the impact of this gigantic event. The method uses a 3D time‐dependent computational ash dispersion model, a set of wind fields, and more than 100 thickness measurements of the CI tephra deposit. Results reveal that the CI eruption dispersed 250–300 km³ of ash over ∼3.7 million km². The injection of such a large quantity of ash (and volatiles) into the atmosphere would have caused a volcanic winter during the Heinrich Event 4, the coldest and driest climatic episode of the Last Glacial period. Fluorine‐bearing leachate from the volcanic ash and acid rain would have further affected food sources and severely impacted Late Middle‐Early Upper Paleolithic groups in Southern and Eastern Europe.