Peatlands of continental western Canada (Alberta, Saskatchewan, and Manitoba) cover 365 157 km2 and store 48.0 Pg of carbon representing 2.1% of the world’s terrestrial carbon within 0.25% of the global landbase. Only a small amount, 0.10 Pg (0.2%) of this carbon, is currently stored in the above-ground biomass. Carbon storage in peatlands has changed significantly since deglaciation. Peatlands began to accumulate carbon around 9000 years ago in this region, after an initial deglacial lag. Carbon accumulation was climatically limited throughout much of continental western Canada by early Holocene maximum insolation. After 6000 BP, carbon accumulation increased significantly, with about half of current stores being reached by 4000 BP. Around 3000 BP carbon accumulation in continental western Canada began to slow as permafrost developed throughout the subarctic and boreal region and the current southern limit of peatlands was reached. Peatlands in continental western Canada continue to increase their total carbon storage today by 19.4 g m−2 year−1, indicating that regionally this ecosystem remains a large carbon sink.