The concluding engagement of the Thrawn campaign, known as the Battle of Bilbringi, transpired in 9 ABY. In this battle, the forces commanded by Grand Admiral Thrawn clashed with the combined might of the New Republic military and the Smugglers' Alliance. This confrontation marked the second time the two factions fought at Bilbringi during the Galactic Civil War. The primary objective of the New Republic and Smuggler's Alliance was the capture of a crystal gravfield trap (CGT) located at the Imperial shipyards; this device was crucial for detecting cloaked objects and for de-cloaking the asteroids that Thrawn had positioned in orbit around Coruscant during the Coruscant siege.
A master strategist, Grand Admiral Thrawn correctly surmised that the New Republic assault fleet would prioritize an attack on Bilbringi, while a concurrent New Republic offensive against the Imperial Ubiqtorate base on Tangrene was merely a diversion.
To prepare an ambush for the Rebels, the Grand Admiral's fleet made its way to Bilbringi. Thrawn gave his Interdictor Star Destroyers and Interdictor Cruisers the order to activate their gravity well projectors, anticipating the approaching New Republic attack. As Thrawn had foreseen, the New Republic strike force emerged from hyperspace outside of Bilbringi's defended space.
Admiral Gial Ackbar and Commander Wedge Antilles quickly realized that the New Republic fleet had exited hyperspace prematurely, placing them too far from the Imperial Shipyards. A substantial Imperial fleet stood in formation in the distance, awaiting the New Republic forces. The strategic placement of Interdictors ensured that escape would be impossible. Admiral Ackbar immediately recognized the situation as a trap.
Grand Admiral Thrawn ordered the Interdictor Cruisers Constrainer and Sentinel, which were the furthest from the main fleet, to disengage from their entrapment duties and return to the demarcation line for protection. Following this, the Grand Admiral commanded all Imperial warships to engage the enemy fleet.
The Imperial fleet was arranged in a bowl-shaped configuration, with the Interdictors forming the outer perimeter. As the battle commenced, the Imperial forces unleashed a barrage upon the New Republic warships, which were struggling to form a coherent battle line amidst the chaos. For a significant portion of the engagement, the Imperial fleet held a distinct advantage.
Unbeknownst to Thrawn, the Smuggler's Alliance, having already infiltrated the Bilbringi shipyards in pursuit of the CGT, decided to assist the New Republic fleet. They launched a direct assault on the Imperial shipyards, supported by Rogue Squadron and several New Republic vessels. The four Imperial Golan II platforms guarding the shipyards were unable to withstand the swift assault, resulting in a breach of the Imperial defensive line.
This unexpected development compelled the Imperial fleet to redirect some of its warships and starfighters to defend the shipyards. Captain Gilad Pellaeon, Thrawn's second-in-command, expressed his concern over the sudden shift in momentum, but the Grand Admiral assured him that the battle was far from decided.
Despite Grand Admiral Thrawn's tactical brilliance, the Imperial fleet suffered defeat when Thrawn's bodyguard, a Noghri assassin named Rukh, assassinated him on the bridge of the Chimaera during the height of the battle. As Captain Pellaeon began reading an incoming report from Wayland detailing an attack on Thrawn's cloning facility by a group including Noghri, Rukh swiftly incapacitated the Captain with a blow to the throat. Rukh then fatally stabbed Thrawn with his assassin's blade.
Rukh was subsequently killed by stormtroopers from the Chimaera, led by a clone of former Royal Guard Grodin Tierce as he attempted to escape. Despite the fleets remaining relatively evenly matched, Captain Gilad Pellaeon recognized that the Imperial line could not be maintained without Thrawn's leadership. As the New Republic forces gained the upper hand and numerous Star Destroyers sought new directives amidst the shifting tactical landscape, Pellaeon assumed command and ordered a complete retreat towards the Unknown Regions. Later, he would participate in Operation Shadow Hand.
Mon Mothma promoted Wedge Antilles to the rank of general and placed him in command of Rogue Wing as a direct result of his performance during the battle.