Anaerobic methanotrophic (ANME) archaea are uncultivated microbes that oxidize the greenhouse gas methane and engage in extracellular electron transfer with other microbes, metal oxides, and electrodes. Here, Ouboter et al. observe strong methane-dependent current associated with high enrichment of ANME archaea on the anode, and provide insights into the mechanisms underlying extracellular electron transfer.