Marine heatwaves (MHWs), discrete but prolonged periods of anomalously warm seawater, can fundamentally restructure marine communities and ecosystems. Although our understanding of these events has improved in recent years, key knowledge gaps hinder our ability to predict how MHWs will affect patterns of biodiversity. Here, we outline a functional trait approach that enables a better understanding of which species and communities will be most vulnerable to MHWs, and how the distribution of species and composition of communities are likely to shift through time. Our perspective allows progress toward unifying extreme events and longer term environmental trends as co-drivers of ecological change, with the incorporation of species traits into our predictions allowing for a greater capacity to make management decisions.