The Imperial Diplomatic Corps, also known as the Diplomatic Service or Diplo-Serv, was a much-honored albeit overlooked branch of the Imperial Military that functioned as a diplomatic body, bringing new worlds into the Galactic Empire and enforcing Imperial standards during Emperor Palpatine's New Order. They often deployed ambassadors and negotiators to hostile worlds to ensure that the occupied populations adhere to the Emperor's orders, and as such reducing the necessity for pacification by force. However, the ambassadors and negotiators were notoriously corrupt, which also ended up costing the Empire by having them accept bribes by Rebel agents.
In 3 BBY, Imperial Intelligence agent Jahan Cross' cover story was that he was assigned to the Diplomatic Service.
Captain Zeta Traal was a member of the Imperial Diplomatic Corps and was assigned to act as an official attaché to the royal regent Zelor on the planet Velmor in 3 ABY.
Following the death of Palpatine at the Battle of Endor, the Imperial Diplomatic Corps found it had acquired a new role—keeping worlds already in the Empire from leaving. This task strained the resources of the Corps, and junior diplomats who would have been closely supervised in the past were given greater autonomy as a result.
In the Fel and Sith Empires, the Diplomatic Corps was under the control of Moff Fehlaaur'aitel'loro, a Chiss. The organization knew Jedi Master Kol Skywalker but knew nothing of his son.