Marine heat waves (MHWs) are long-lasting extremely warm water phenomena in the ocean that have a devastating effect on marine ecosystems. A comprehensive knowledge of the physical processes governing the life cycles of MHWs is crucial for improving the forecasting capacity of MHWs, but is still lacking. Here, we use a historical simulation from an eddy-resolved global climate model with improved MHW representation and show that heat flux convergence by oceanic mesoscale eddies acts as the dominant driver of MHW life cycles in most parts of the global ocean. In particular, mesoscale eddies contribute significantly to the growth and decay of MHWs, whose characteristic spatial scale is comparable or even larger than that of mesoscale eddies. The effect of mesoscale eddies is spatially heterogeneous, increasingly dominant in the western boundary currents and their extensions, in the Southern Ocean, as well as in the eastern boundary upwelling systems. This study reveals the key role of mesoscale eddies in driving global MHW life cycles and highlights that using ocean models to resolve eddies is necessary, although not necessarily entirely sufficient, for accurate MHW predictions. Marine heat waves (MHWs) are extremely warm water phenomena in the ocean. They cause serious environmental and socio-economic impacts, including loss of biodiversity, reductions in catch rates, damage to aquaculture, as well as changes in species behaviour. Satellite observations have revealed significant increases in the frequency, duration, and intensity of MHWs over the past few decades in most parts of the global ocean, primarily due to gradual sea surface warming caused by increasing greenhouse gas emissions. (Ce Bian, Zhao Jing, Hong Wang, Lixin Wu, Zhaouhi Chen, BOlan Gan, Haiyuan Yang, Nature Communications)