The demographic effects of rapid environmental change and extreme climatic events (ECEs) can cascade across trophic levels, while the potential evolutionary implications have rarely been explored empirically. Here, we show how an ECE in high Arctic Svalbard triggered a trophic chain reaction, affecting overwintering and migratory vertebrates, which eventually induced a shift in density-dependent phenotypic selection in barnacle geese. A record-breaking rain-on-snow event and ice-locked pastures led to reindeer mass starvation and a population crash, followed by a period of low mortality and population recovery. This caused lagged, long-lasting reductions in reindeer carrion numbers and resultant low abundances of the Arctic fox, a scavenger on reindeer and predator of migratory birds. The associated shift in gosling predation rates by Arctic foxes allowed for a rapid increase in barnacle goose population density. As expected from r- and K-selection theory, we show that the goose body condition maximising Malthusian fitness increased with this shift in population density. Thus, the ECE acting directly on the overwintering community indirectly led to selection for larger geese. This high Arctic case study provides rare empirical evidence of links between ECEs, community dynamics and evolution, with implications for how we understand the indirect eco-evolutionary impacts of global change.