The Chancellery Guard were Time Lords who served mainly as Policemen on the planet Gallifrey. They would normally be armed with staser guns.
The Chancellery Guards were the main police service of Gallifrey, the only beings allowed to carry arms inside of the Citadel.
They would do normal police tasks such as criminal investagations and protection for the Time Lords of Gallifrey.
During the last great Time War the Time Lord's although wise and Masters of time travel, they did not posses much weaponary.
Most of the Chancellery Guard's lacked actual combat experience. Although they still took part in the fight against the Daleks. Although the Time Lord's main weapons were defensive shields used to destroy any attacking Daleks.
They were killed when the Time Lord known as the Doctor ended the war when the Time Lord President went mad and no claer victory was in sight for both races.