Deep Space 3 was a Federation Starbase constructed prior to 2290 near the border of the Klingon Empire, with the purpose of keeping an eye on the Breen and other species in Breen space, in the vicinity of the Alpha Quadrant's Black Cluster. (TOS novel: War Dragons; ST reference: Star Charts)
In 2290, the space station was attacked by combined Anjiri and Nykkus forces, resulting in great damage, with the USS Enterprise-A and USS Excelsior taking part in the station's defense. (TOS novel: War Dragons)
By 2370, the station was under the command of Admiral Marcus Holt. In that year, the station hosted the annual palio, wherein the Ferengi were accused of trying to bribe the Breen pilot into throwing the race.
By 2381, Deep Space 3 was under the command of Commander Gong. DS3 was the location of a field office of the Starfleet Corps of Engineers, directed by Lieutenant Commander Kareem Mussad. Shortly after the Borg Invasion of 2381, Deep Space 3 became a central research facility for "Project Reassimilation", a classified project to study deactivated Borg technology and attempt to adapt it for Starfleet use. (ST novel: A Singular Destiny)