The record-breaking annual mean global sea surface temperature in 2024 fueled extensive marine heatwaves (MHWs) across global coral reef zones, yet their spatiotemporal characteristics have not been comprehensively quantified. Here, we show that during the 2024 warm season, MHW total duration and cumulative intensity exceeded the historical mean by more than three standard deviations. Widespread and persistent MHWs occurred across major coral reef regions, particularly in the Red Sea, Coral Triangle, Fiji, the Caribbean, and Brazil. Most coral biogeographic provinces experienced significant increases in the frequency of Moderate, Strong, and Severe MHW categories relative to the 1985–2024 climatology. These extreme events were associated with substantial accumulation of ocean heat content in the Indo-Pacific warm pool and tropical Atlantic following the transition from the triple-dip La Niña (2020–2023) to the 2023–2024 El Niño. Regional oceanographic conditions further modulated the intensity and drivers of warm-season MHWs in 2024.