Earthworm invasion in North American forests can alter soil functioning. We investigated how the presence of invasive earthworms affected microbial communities, key drivers of soil biogeochemistry, across the major soil types of the Canadian boreal forest, which is a region largely understudied. Although total microbial biomass did not change, community composition shifted in earthworm-invaded mineral soils, where we also found higher fungal biomass and greater microbial species diversity.