During the Galactic Civil War, Gaarn held the rank of admiral within the Galactic Empire. Not long after the Battle of Endor, he received orders to safeguard the Eclipse, a Super Star Destroyer in orbit around Kuat. This protection mission became critical when the forces of the Zann Consortium, under the command of crime lord Tyber Zann, launched an attack. Gaarn, operating from his command ship, the Executor-class Star Dreadnought Annihilator, commanded a small fleet consisting of three Imperial-class Star Destroyers in an attempt to push back the Consortium assault. Despite their efforts, the Imperial forces suffered a defeat, and the Annihilator met its end.
Admiral Gaarn loyally served the Galactic Empire throughout the Galactic Civil War. In the year 4 ABY, shortly following the pivotal Battle of Endor, the Zann Consortium, a criminal syndicate spearheaded by the notorious crime lord Tyber Zann, initiated an attack upon the Imperial shipyards stationed above the planet of Kuat. Their objective was to seize control of the formidable Super Star Destroyer known as the Eclipse. Gaarn, leading a small fleet of three Imperial-class Star Destroyers from his flagship, the Executor-class Star Dreadnought Annihilator, moved to reinforce the beleaguered Imperial forces defending Kuat.
Gaarn's warships engaged the Zann Consortium's forces, who had successfully infiltrated and taken command of the Eclipse. The primary objective of the Annihilator was to eliminate the massive warship before it could be turned against the Imperial fleet. However, the Consortium's forces proved too strong, ultimately destroying the Annihilator and the remaining Imperial ships. This victory allowed Zann to access the valuable data archives stored within the Eclipse.
Gaarn's character was conceived for the 2006 LucasArts real-time strategy video game Star Wars: Empire at War: Forces of Corruption. This game served as an expansion to the original Star Wars: Empire at War video game. Although Gaarn does not make a direct appearance in Forces of Corruption, his name is mentioned in the information box associated with the Annihilator. This information can be accessed by hovering the player's cursor over the ship during gameplay. Gaarn's command ship is featured in the final level of the campaign, serving as the ultimate enemy. While the game requires the destruction of the Annihilator, the fate of Gaarn himself remains ambiguous, although his death is the most likely outcome.