Montgomery was a 23rd century Starfleet operations division security officer serving aboard the USS Enterprise under Captain James T. Kirk.
In 2267, he stood guard on the bridge during the Enterprise's search for the USS Constellation and during its later encounter with the planet killer.
Montgomery was later assigned by Spock to escort Commodore Matthew Decker to Sickbay. En route, Decker attacked and overpowered Montgomery, in one of the corridors outside the turbolift, and afterward dragged Montgomery's unconscious body into an adjacent room. (TOS: "The Doomsday Machine")
In 2268, when the Vulcan Ambassador Sarek and his party came aboard, he was amongst the honor guard. (TOS: "Journey to Babel")