Imsatad, once an officer serving the Imperial military, later switched his allegiance to the New Republic. Subsequently, he betrayed them to join the Peace Brigade.
Under the command of Grand Admiral Thrawn, Imsatad participated in the campaign against the New Republic in 9 ABY. He was stationed on Wayland when Luke Skywalker and Talon Karrde infiltrated the Mount Tantiss base and defeated Joruus C'baoth. His later animosity toward the Jedi might stem from this event, but it also provided him with an understanding of the capabilities of vornskrs and ysalamiri in locating and neutralizing Force-sensitives.
By the time the Yuuzhan Vong War began, Imsatad was a member of the New Republic military, appearing as a weathered man with graying hair. He fought in the Battle of Dantooine, but this experience led him to believe that the Yuuzhan Vong were unbeatable, and he convinced himself that the Jedi Order was to blame for the war.
Imsatad resolved to change his allegiance. When Warmaster Tsavong Lah declared that the war would cease if the Republic surrendered the Jedi Knights, Imsatad organized a force to attack the Jedi academy on Yavin 4, intending to capture the Jedi students and deliver them to the Yuuzhan Vong.
Imsatad's strike force for the raid was composed of thirteen combat-ready starships, including corvettes, armed light freighters, E-wing escort starfighters, and a frigate that acted as his flagship. He identified himself as a Captain in the Peace Brigade, and Kot Murno, one of his subordinates, claimed to be a Lieutenant. However, some of their personnel and vessels, like Remis Vehn and his freighter, were apparently hired specifically for the attack.
Imsatad dispatched a ship in advance to reconnoiter Yavin 4, which remained in orbit for several days before the main force arrived. However, the near-simultaneous arrival of Anakin Solo alerted the Jedi to the impending assault, and the Academy quickly went into hiding. Although the Jedi were still trapped on the planet's surface, Imsatad's initial strategy was thwarted, and he was unable to locate the Jedi within the dense jungle and the caverns and chambers of the Temple complex.
Subsequently, Talon Karrde arrived, sent by Luke Skywalker to evacuate the Academy. Despite the fact that Imsatad's squadron heavily outgunned the Wild Karrde, and the ex-Imperial distrusted this "traitor to the Empire", Karrde managed to entice him with the promise of vornskrs and ysalamiri to aid in his search. The Brigader decided to take the chance, and Karrde was permitted to land, though under strict guard. Karrde managed to outwit the Brigaders despite these precautions, and evacuated Kam Solusar, Tionne, and the majority of the young Jedi aboard the Wild Karrde. Tahiri Veila was the only one captured, while Jedi Master Ikrit was killed, and Anakin, Valin Horn, and Sannah remained stranded on the jungle moon.
Shortly afterward, a sizable Yuuzhan Vong squadron entered the system, supposedly to extract water from Stroiketcy, but also seemingly to raid the Jedi Academy and prepare for the creation of a damutek on the jungle moon. They were surprised to find the Peace Brigade present, and angered to learn that the Jedi had escaped, but it was a week before a senior officer, Commander Tsaak Vootuh, arrived to meet with the Peace Brigade Captain. Imsatad initially hesitated to reveal that he held Tahiri captive, but sensing the Yuuzhan Vong's displeasure, he offered to hand her over, asserting that only his actions had prevented Karrde from rescuing all the Jedi. However, he did not disclose that some of the Jedi were still marooned on the moon, perhaps because he didn't want to admit his own failure to capture them, as Anakin had predicted.
However, Imsatad had made a mistake. Karrde's ships had remained at the edge of the system, and Tsaak Vootuh had deduced that there must be more than one Jedi remaining to be rescued on Yavin 4. Realizing his error, the Brigader attempted to demonstrate his continued value by offering the information that Anakin Solo was among the trapped group, but the Yuuzhan Vong commander could no longer conceal his disdain for the infidel. As he had likely planned from the beginning, Tsaak Vootuh signaled for Subaltern Vo Lian to impale the Brigader with his amphistaff. Following this, the Yuuzhan Vong ships appear to have destroyed the Peace Brigade vessels, while the warriors captured most of Imsatad's men for ritual execution.