During the Mandalorian Wars, the Leviathan functioned as an Interdictor-class cruiser within the Republic Navy. As the Jedi Civil War began, it transitioned into the flagship of Saul Karath, a former Republic Admiral. Karath then served the Sith Empire under Darth Revan and, subsequently, Darth Malak. This warship participated in several pivotal engagements during the latter conflict, notably the Attack on the Endar Spire, the ensuing blockade of Taris, and the skirmish that resulted in the death of its commanding officer.
Mirroring other capital ships within the Sith fleet, the Leviathan had origins as a Republic Navy vessel. Serving as a potential technological precursor to later Star Destroyers, the Leviathan was one of many vessels designed similarly and commissioned by the Republic for use in the Mandalorian Wars. The Leviathan held the distinction of being the sole ship of its class to emerge from the Corellian shipyards in a spaceworthy state.
The _Interdictor-class cruiser Leviathan extended 600 meters, equipped with four massive gravity-well projectors, providing the capability to extract vessels from hyperspace. Although considered rudimentary by future standards, it represented the apex of interdiction technology for its time. Furthermore, it featured 20 quad laser cannons, a tractor beam projector, four turbolaser batteries, and two ion cannons.
After Saul Karath's defection brought the Leviathan into the service of the Sith, the ship accommodated two squadrons of Sith fighters. It is probable that Darth Malak launched his assault on his master's ship from this vessel, rendering him unconscious before the Jedi captured him. Subsequently, during Malak's pursuit of Bastila Shan, he employed the Leviathan's quad laser cannons to devastate a significant portion of Taris's Upper City.
The tractor beam played a role in another attempt to seize Bastila Shan, as well as the reformed Revan. The beam facilitated the boarding of the Ebon Hawk and the capture of the two Jedi, who were subsequently imprisoned. Following a rigorous interrogation, Revan managed to escape and navigate to the bridge, situated adjacent to the command deck. The bridge door was sealed, but Revan and his companions donned spacesuits and utilized an airlock that opened onto an external walkway providing bridge access. After securing the bridge, Revan, Bastila Shan, and Carth Onasi eliminated Admiral Karath and disengaged the tractor beam holding the Ebon Hawk within the hangar. During Revan and his companions' escape attempt, they encountered Malak, leading to a lightsaber duel between the former master and apprentice. Malak gained the advantage, trapping Revan in Force stasis. However, Bastila intervened, preventing Malak from killing Revan and choosing to confront Malak so Revan and Carth could escape.
It is likely that the Leviathan met its end during the battle of Rakata Prime, as its computer systems indicated the Star Forge as its destination when Revan manipulated the systems to enable the Ebon Hawk's escape.
Following the loss of the Leviathan, the Ravager and numerous other "proto-Star Destroyers" to Revan and Malak's Sith Empire, the Republic abandoned the design, possibly due to resource constraints. Instead, they opted for capital ships that aligned more aesthetically with the Republic's peaceful era, such as the Hammerhead-class cruiser.
During the Taris sequence, Darth Malak's dialogue with Saul suggests the presence of an entire fleet orbiting the planet. However, only the Leviathan is visible. This holds true in the cinematic depictions of Taris's destruction and the view from the Leviathan's bridge. Conversely, while operating the gun turret on the Ebon Hawk, a fleet comprising twelve ships can be observed in orbit around Taris. Their size and immobility preclude them from being fighters. Based on their form, they seem to be Sith Interdictor Cruisers, belonging to the same class as the Leviathan.
According to John Jackson Miller (who was not involved in the game's development), the name Leviathan was inspired by the United Kingdom Royal Navy's 18th-century Leviathan-class ships, which were designed based on the captured French 74-gun warship Courageux. Miller later used the name Courageous in the KotOR comic series for Courageous, Saul Karath's battleship in 3964 BBY (although it did not share the same design as the Leviathan).