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The soils of the Maritime and sub‐Antarctic experience extreme environmental conditions but nonetheless host biological communities that can survive low temperatures, limited water availability and short day lengths or even the complete absence of solar radiation during the winter. We determined the soil organic carbon (SOC) and total nitrogen (N), soil microbial biomass (SMB), labile carbon (LC) and respiration rate (RR) in soil samples from the longest latitudinal transect (approximately 2,000 km) ever sampled exclusively in the Maritime and sub‐Antarctic, comprising 69 sites located between South Georgia (54°S) and south‐eastern Alexander Island (72°S). With the exception of the most northerly location (South Georgia), the greatest SMB values occurred at 67–68°S, despite the harsh environmental conditions. This is consistent with the relative nutrient richness of the soils at these latitudes, as indicated by large SOC and total soil N concentrations, which are in turn probably linked to more abundant guano and excreta deposition by sea birds and seals, which have fewer and smaller areas of ice‐free terrain to land or haul out on further south. South of 68°S, SOC values declined with increasing latitude, which is probably due to increasingly extreme environmental conditions. We also found that the SOC and SMB values, the proportion of SOC considered labile (LC/SOC) and the carbon mineralization rates expressed as either RR/SOC or RR/SMB were all small compared with values from less extreme temperate and tropical regions. However, the proportion of the SOC in the microbial biomass (SMB/SOC) was substantially greater than that reported for non‐polar soils. We conclude that although the soils of the Maritime and sub‐Antarctic have small and relatively inactive microbial communities, they are characterized by efficient conversion of organic resources into microbial biomass and large affinities for added substrates. Highlights: Soil carbon parameters are reported from sites along the longest latitudinal transect in Antarctica ever sampled.The soil microbial biomass tended to peak at 67–68°S, coinciding with relative SOC and N abundance in the soil, probably arising from guano and excreta from sea birds and mammals.The soil microbial community was small but highly efficient at converting organic resources into microbial biomass, as indicated by large microbial biomass/soil organic carbon ratios. [ABSTRACT FROM AUTHOR]