This study demonstrates the existence of a microbial consortium capable of coupling anaerobic methane oxidation (AOM) to denitrification. The consortium, enriched from anoxic sediments, oxidizes methane to carbon dioxide while simultaneously denitrifying nitrate in the absence of oxygen. The consortium consists of a bacterium from an uncharacterized phylum and an archaeon distantly related to marine methanotrophic Archaea. The ability to perform this reaction was confirmed through various experiments, including continuous monitoring of oxygen levels, lipid analysis, and 16S rRNA gene sequencing. The consortium's activity was also detected in different freshwater ecosystems, suggesting a significant contribution to global biogeochemical cycles. This finding challenges the previous understanding that AOM coupled to denitrification is not possible in nature and highlights the potential for this process to influence methane and nitrogen cycling in agricultural and freshwater environments.This study demonstrates the existence of a microbial consortium capable of coupling anaerobic methane oxidation (AOM) to denitrification. The consortium, enriched from anoxic sediments, oxidizes methane to carbon dioxide while simultaneously denitrifying nitrate in the absence of oxygen. The consortium consists of a bacterium from an uncharacterized phylum and an archaeon distantly related to marine methanotrophic Archaea. The ability to perform this reaction was confirmed through various experiments, including continuous monitoring of oxygen levels, lipid analysis, and 16S rRNA gene sequencing. The consortium's activity was also detected in different freshwater ecosystems, suggesting a significant contribution to global biogeochemical cycles. This finding challenges the previous understanding that AOM coupled to denitrification is not possible in nature and highlights the potential for this process to influence methane and nitrogen cycling in agricultural and freshwater environments.