Mobile genetic elements (MGEs), such as viruses and plasmids, drive the evolution and adaptation of their cellular hosts from all three domains of life. This includes microorganisms thriving in the most extreme environments, like deep-sea hydrothermal vents. However, our knowledge about MGEs still remains relatively sparse in these abyssal ecosystems. Here we report the isolation, sequencing, assembly, and functional annotation of pMO1, a 28.2 kbp plasmid associated with the reference strain Marinitoga okinawensis. Carrying restriction/modification and chemotaxis protein-encoding genes, pMO1 likely affects its host's phenotype and represents the first non-cryptic plasmid described among the phylum Thermotogota.