The Lioaoin pirate campaign was a series of operations that involved Lioaoin pirates and the Chiss Ascendancy, not long after the formation of the Chiss Expansionary Defense Fleet.
The economy of the Lioaoin Regime had faltered, causing that Regime to turn to privateering to survive. As a result, Lioaoin pirates became a serious threat to trade, commerce, and diplomacy in the Unknown Regions near Lioaoin space. Lioaoin pirates attacked civilians and military of various peoples of the Chaos including the Chiss and the Garwians. The Chiss Ascendancy became concerned and wanted to put an end to those pirate attacks, but had not proven who was behind them.
Some time after his cheating allegation and subsequent graduation from the Taharim Academy, Junior Commander Mitth'raw'nuru served as a pilot for the Chiss Expansionary Defense Fleet. While serving in that capacity, he served as pilot for a Chiss diplomatic mission to Bardram Scoft, the homeworld of the Scofti species. That journey was navigated by Qilori of Uandualon, a Pathfinder of the Navigators' Guild.
There, Thrawn saw Lioaoi vessels that to him artistically resembled the pirate ships that had been attacking the Ascendancy. He asked Qilori what nation the vessels represented. The Pathfinder confirmed that they were Lioaoin, and Thrawn surmised that Qilori knew more than he had let on about the Lioaoin Regime's involvement with pirates. He proceeded to further research the Pathfinders and their abilities, thus uncovering their secret ability to track each other through hyperspace.
Some time later, Junior Commander Thrawn suspected that the pirates were sanctioned by the Lioaoin Regime, but was unable to prove this. As such, the Chiss non-aggression protocols prohibited retaliation against the Lioaoin government. He once again hired Qilori to guide a convoy of three Chiss ships to the Lioaoin heartworld. At the Lioaoin heartworld, Thrawn purposely declared he had found the pirates in a trade language understandable to the Lioaoi, so they would know for certain that he was hunting pirates.
Thrawn was aware of the Pathfinders' ability to track each-other through hyperspace, which was supposed to be a closely guarded secret. Thrawn used that knowledge to engage the Lioaoin pirates without violating the Ascendancy's preemptive-strike laws. He had specifically hired a Pathfinder navigator because he knew from the "style" of Lioaoin pirate attacks that the pirates used Pathfinders to navigate.
He and Qilori jumped through hyperspace to Kinoss, where four Lioaoin corsairs guided by Pathfinders soon followed to attack the apparently fleeing Chiss. This was Thrawn's goal, as he laid a trap at Kinoss. A Chiss warship, commanded by Mid Captain Irizi'ar'alani (Ziara), appeared amongst the Lioaoin corsairs and destroyed them.
If Thrawn had been wrong and they would not be pursued by pirates through hyperspace, no harm would have been done as Thrawn had been piloting an unarmed freighter. However, the pirates tracked him and attacked the Chiss within the borders of the Ascendancy, allowing the Chiss Defense Force to engage them. As a result of his success at Kinoss, General Ba'kif promoted Thrawn by two ranks; skipping Mid Commander and directly attaining Senior Commander rank. Ba'kif also promoted Ziara to Senior Captain for her role in the mission.
The next year, Senior Captain Ziara's patrol cruiser Parala received a distress signal from the Garwian colony world of Stivic which was under attack by Lioaoin pirates. Senior Commander Thrawn implored Ziara to intervene, but the non-interference policy of the Ascendancy prevented the Chiss from engaging the Lioaoins, even to assist in the Garwians' defense. However, part of the mission of the Expansionary Defense Fleet was to discover, assess, and observe external threats to the Ascendancy. As such, the Parala was permitted to observe the attack (and would be permitted to provide humanitarian aid in its aftermath).
Ar'alani agreed to observe the Lioaoin attack on Stivic, and the Parala exited hyperspace above that planet. Thrawn wished to defend the Garwians in spite of the non-aggression protocols, insisting he could tell Ziara how to defeat the pirates with no damage to the Parala. Ziara did not allow Thrawn to engage the Lioaoi, but allowed him to "calibrate" the Paralas ranging lasers, which did not require calibration. Thrawn took the opportunity to send a message to the Garwians via modulated laserfire, instructing them on the attacking corsairs' weaknesses. As a result, the tide of the battle turned, and the Garwians destroyed three of their four attackers.
Some time after the Stivic incident, Ziara had been promoted to the flag rank of commodore and as a result was no longer a member of the Irizi family. The ruling Ruleri body of the Garwian Unity invited Commodore Ar'alani and Senior Commander Thrawn to the Garwian homeworld of Solitair to be thanked and honored in person. Unbeknownst to Thrawn and Ar'alani, the Lioaoin Regime planned to send diplomats to Solitair to negotiate their Regime's surrender to the Garwian Unity.
Upon the arrival of the Lioaoi, the Garwians pretended to be under attack. Security Chief Frangelic rushed his Chiss guests to a war room in the Solitair planetary security center. There, the Garwian military officers begged Thrawn to aid their "defense". In reality, the Garwians were jamming the Chiss' communications with the Chiss heavy cruiser Destrama to feed the illusion that Solitair was under attack. Ar'alani discovered this, and Thrawn demanded the Garwians lift the jamming. Once the jamming was lifted, it was revealed that the Lioaoi had come to surrender, but the Garwians attacked them and sought to conquer some of Lioaoin space. The Chiss, infuriated at their hosts' manipulation, warned the Garwains to hope they never meet the Chiss again.
Some time later, Thrawn would be promoted to Senior Captain and lead the Vagaari pirate operations. The Vagaari pirate operations were remembered as militarily successful but politically disastrous by Syndics Irizi'stal'mustro "Zistalmu" and Mitth'urf'ianico "Thurfian."
The Lioaoin pirate campaign appeared in various flashbacks in the 2020 novel Thrawn Ascendancy: Chaos Rising by Timothy Zahn. The flashbacks provided context for the novel's main events as well as the personalities and history of various characters.