A better understanding of community dynamics and ecosystem functioning can be achieved by describing how community functional structure responds to environmental change over both time and space and by identifying which functional groups best mediate community responses. Here, we used a trait-based approach in combination with a newly developed application of principal response curves to functionally characterize a rapid taxonomic shift in the eastern English Channel fish community in the late 1990s. We identified the functional groups with the greatest contributions to the overall shift in fish functional structure and uncovered significant trait−environment relationships. We found that pelagic species with rapid life history cycles, characterized by broadcast spawning, small offspring size, and early maturation, declined considerably in abundance following an increase in sea surface temperature associated with a warming phase of the Atlantic Multidecadal Oscillation, which was likely exacerbated by historical fishing pressure. In contrast, species with late maturation, high parental care, and few, well-developed offspring increased in abundance, reinforcing that fish community responses to climate warming are strongly mediated through life history traits. By examining how environmental factors drove a community shift at the trait level, we provide a mechanistic understanding of how fish functional structure responds to rapid environmental change.