Garrett was Starfleet officer in the late 23rd century.
In 2285, he was CO of Starbase 13. There, he was informed of a computer made by the ISS Enterprise and informed Captain March of the USS Courageous of this. Following the lost of communications with the Courageous, Garrett then ordered a red alert for all personnel and prepared the starbase for defense against the ISS Enterprise.
Following the defeat of the Imperial Starfleet armada, Garrett then had a brief interview with reporter Lyndra Dean but could not tell her of the Terran Empire's attempted invasion. (TOS - The Mirror Universe Saga comics: "Double Image", "Homecoming...")