In the mirror universe, the Tellarites were a subject species of the Terran Empire.

The Tellarites were conquered some time following the conquest of the Alpha Centaurans in 2074. Although technologically savvy and costing the empire many lives to subdue, the Tellarites were eventually brought to kneel. Following their surrender, they were offered client status where they would allowed to live so long as they willingly gave over their special skills to the benefit of the empire. Continuous threats regarding the destruction of their homeworld should their engineering ingenuity ever fail resulted in the quick advancement of the empire's technology. (Decipher RPG module: Through a Glass, Darkly)

By the mid 2150s, Tellarites could be found serving on board Imperial Starfleet vessels such as the ISS Enterprise (NX-01). (ENT episode: "In a Mirror, Darkly")

With the rise of the Klingon-Cardassian Alliance, the Tellarites would suffer even more than thay had under the empire. As the Alliance found Tellarites to be far too argumentative and difficult to deal with, they were openly attacked and reduced to only a few hundred thousand by the 2360s and 2370s. (Decipher RPG module: Through a Glass, Darkly)