Sivill, a Human of the male sex, held the rank of Captain and was in command of a Sith warship. This vessel belonged to the navy of the Sith Empire that had resurfaced following the Treaty of Coruscant's signing. During a brief battle in the Kuat sector with a Republic transport ship, he spearheaded the boarding party that successfully captured Jedi Master Dar'Nala.
During the Great Galactic War, Sivill was the commanding officer of a Sith military vessel. Following the signing of the Treaty of Coruscant, Darth Baras, a Sith Lord, secretly instructed Sivill to launch an attack on the Envoy, a vessel transporting Satele Shan and Dar'Nala, both Jedi, in the Kuat sector within the Core Worlds. The aim was to make it appear as though the Republic had initiated the conflict. Sivill addressed the crew via the ship's communication system, announcing an attack by a Republic vessel and the necessity of a boarding party to capture at least one Jedi alive.
Sivill led a team of Imperial commandos onto the transport, where some were engaged and killed by Satele Shan. Sivill and the remaining commandos confronted Dar'Nala, taunting her that she wouldn't die heroically because they needed to talk, before ensnaring her in a net. Dar'Nala urged Shan to escape and inform the Jedi Council of the attack. Shan fled, leaving Dar'Nala as Sivill's captive.
Subsequently, Sivill interrogated the Togruta Jedi Master within the detention area of an Imperial vessel. During the interrogation, he attempted to coerce Dar'Nala into admitting that the Envoy had fired first on the Sith warship by subjecting her to electric shock treatment. Dar'Nala refused to comply, prompting him to leave, promising one final opportunity upon his return.
Later on, Dar'Nala assisted another Sith captive in escaping, with the intention that he would reveal the truth to the Republic. Sivill was enraged, and since Dar'Nala had refused to cooperate, he ordered her execution... or so he believed.
Sivill later perished in a bombing on Korriban, an event that Darth Angral later discovered was orchestrated by Baras.