Sarsh, a Force-sensitive being, functioned as a navigator and Pathfinder within the ranks of the Navigators' Guild. In the year 18 BBY, the Grysk agent known as "Jixtus" contracted Sarsh, along with fellow Pathfinder Qilori, to pilot the Kilji picket cruiser named Hammer and the Kilji war cruiser called Anvil, respectively. Their destination was the Rapacc system situated in the Unknown Regions. Upon the starships' arrival at their designated star system, the Anvil was obliterated by the Chiss heavy cruiser Springhawk, causing the Hammer to escape into the Unknown Regions' "Sunrise" system.
Qilori, having used an escape pod to survive the Anvil's destruction, was rescued by Senior Captain Mitth'raw'nuruodo, also known by his core name "Thrawn," who commanded the Springhawk. Under Thrawn's orders, Qilori employed the Force to locate Sarsh, which led them to the Paccosh-commandeered Nikardun blockade frigate Aelos in the Sunrise system. There, the frigate's crew boarded the Hammer. Following Thrawn's instructions for Sarsh to acquire Kilji data, the group departed from the picket cruiser. Soon after, the Pathfinder utilized a Paccian troop transport, jumping in and out of hyperspace to determine the arrival time of Jixtus's fleet at the system.
Sarsh, possessing Force-sensitivity, was enlisted by the Pathfinders, a division of navigators serving the Navigators' Guild. After joining, he encountered fellow Pathfinder Qilori before their assignments to separate starships. In 18 BBY, the Grysk operative "Jixtus" engaged Sarsh and Qilori to navigate two cruisers belonging to the Kilji Illumine nation: the Kilji picket cruiser Hammer and the Kilji war cruiser Anvil. These vessels formed part of the task force commanded by Illumine General Crofyp. Sarsh and Qilori guided the Hammer and Anvil, respectively, transporting these Kilji warships to the Rapacc system located within the Unknown Regions.
Subsequently, the Kilji force engaged in combat against the Chiss heavy cruiser Springhawk and the Paccosh-commandeered Nikardun blockade frigate Aelos. While Qilori managed to escape the destruction of his cruiser via an escape pod, the Hammer fled to a system in the Unknown Regions known as the "Sunrise" system. Senior Captain Mitth'raw'nuruodo, the Chiss commander of the Springhawk and also known by his core name "Thrawn," rescued Qilori and instructed him to use the Force to locate Sarsh.
The Hammer soon arrived in the Sunrise system, maintaining position with one of Jixtus's warships. Shortly after, the Aelos arrived, and its crew—comprising Thrawn, Qilori, and a squad of Paccian commandos—boarded the picket cruiser. The commandos swiftly killed all Kilji on board, sparing Sarsh, who was located on the Hammer's bridge. Thrawn communicated with Sarsh in the Taarja trade language, tasking him with gathering data on the Illumine's battle fleet, known as the Illumine Kilhorde.
This request surprised the Pathfinder, who initially refused due to the Navigators' Guild's prohibition against collecting ship data. However, he relented after Thrawn suggested he might not be worth taking along, providing the Chiss with a Kilji data rectangle containing the requested data. As the boarding party prepared to return to the Aelos, Thrawn instructed Qilori to ensure his fellow Pathfinder remained quiet and compliant. After Jixtus's warship departed, the group took refuge in a mining compound on the planet "Sunrise," situated within the system of the same name.
Shortly thereafter, Qilori left the planet and reported to Jixtus. Jixtus asked Qilori to explain how Sarsh survived the Hammer's destruction the next time they spoke. While Jixtus's fleet made its way to the Sunrise system, Sarsh remained aboard a Paccian troop transport in the outer system, repeatedly jumping the troop transport into and out of hyperspace to inform Thrawn of the Grysk fleet's arrival. After Thrawn's fleet destroyed the Grysk force, Qilori, who thought Sarsh had perished, was instructed by Thrawn to return his fellow Pathfinder to the Navigators' Guild Concourse 447 space station.
Sarsh made his debut in the 2021 novel Thrawn Ascendancy: Lesser Evil, the concluding book in Timothy Zahn's Star Wars: The Ascendancy Trilogy.