Soil organic matter (SOM) plays an important role in mitigating climate change and sustaining soil health and food production 1,2. Mounting evidence suggests that microbial necromass is the main contributor to SOM 3; however, we lack quantification of microbial necromass at a global scale, especially in subsoils. Here, we generate, for the first time, global distribution maps of microbial necromass carbon (C) and nitrogen (N) and contributions to SOM in topsoil and subsoil. Globally, necromass concentrations varied widely across ecosystems and by latitude, contributing 19-60% to SOC and 41-92% to soil N stocks, with particularly large accumulations in boreal and tropical ecosystems. On average, fungal necromass contributions to SOM are 3x greater than bacterial, although this varied across ecosystems. Microbial necromass contributions to SOC are strongly associated with soil C:N ratios and pH; necromass contributions are greater in soils with narrow C:N ratios and higher pH. Microbial necromass is on average 23 and 77 times greater than living microbial biomass in topsoil and subsoil, respectively. These data highlight the importance of necromass contributions to SOM, especially soil N, and the need for spatially resolved necromass data sets that can be used in biogeochemical models to estimate SOM dynamics more accurately.