From Halopedia, the Halo wiki
The Chancellor's Guards were considered a threat to the BIA at the outset of the Human-Covenant War. In 2526, the UNSC initiated Operation: SILENT STORM, intending to use Biko and its moon Seoba as distractions for the Fleet of Inexorable Obedience. When Task Force Yama discovered an insurrectionist camp in their intended staging area, operative personnel were instructed to identify themselves as the Chancellor's Guards Battalion Five to ensure that SILENT STORM's secrecy was not breached.
Shortly following the Battle of Seoba, the Chancellor's Guards joined UNSC Navy forces in the Battle of Biko, defending the planet against the Fleet of Inexorable Obedience. Unfortunately, the Bikon fleet only numbered roughly fifty patrol frigates, and could do little to stop the might of several Covenant warships. The organisation was presumably disbanded after the planet's fall.
The Chancellor's Guards had units operating at least on the battalion level, suggesting they had several thousand armed personnel. The Chancellor's Guards presumably operated the fifty-or-so patrol frigates assigned to protect the space around Biko.
List of appearances