Barnhart was a male Human Starfleet crewman who lived during the mid-23rd century. He served aboard the USS Enterprise under Captain James T. Kirk, during a historic five-year mission that starship undertook.
In 2266, Barnhart was performing maintenance on the ship's atmospheric system when he became one of a number of Enterprise crewmembers killed by a creature which had infiltrated the ship and was extracting all of the sodium chloride from its victims. Barnhart's body was found on deck nine, section two. (TOS: "The Man Trap")