Noah and Basch lived and grew up in the Republic of Landis before it was invaded by the Empire. During the invasion, Basch fled their hometown to the Kingdom of Dalmasca to serve with the military, while Noah moved with his sickly mother to Archadia, her homeland. There, he adopted his mother's surname, Gabranth, and joined the Archadian Military. He quickly climbed the ranks, and with the backing of Emperor Gramis became Judge Magister. Gabranth was placed in charge of the 9th Bureau, primarily concerned with the gathering and dissemination of information for the Emperor.
Two years before the main events of Final Fantasy XII, Gabranth was present at Nalbina Fortress where he killed King Raminas of Dalmasca while impersonating his brother, Basch. In the manga adaptation of Final Fantasy XII, Vayne orders Gabranth to do this, believing Basch's treachery and Raminas's death will give him an excuse to suspend peace negotiations and push his father to take over Dalmasca in full. The two spread rumors of an assassination attempt on the king's life to trick Basch and a force of his soldiers to storm the Fortress and "rescue" Raminas. In reality this was a ruse to get Basch at the scene: Gabranth poses as Basch and attacks the Dalmascan officials present, killing them before pursuing Raminas. The two run into Basch and Gabranth engages him, giving Basch a facial scar over his left eye before defeating him. Gabranth then kills Raminas, and to ensure that the trick is successful, one of Basch's soldiers, Reks, witnesses Gabranth (as Basch) confess to the murder. For the next two years, Basch would be locked up in the Nalbina Dungeon framed for regicide, Gabranth visiting regularly to interrogate him about the Resistance that rose to oppose the Empire.
With Raminas dead, the peace negotiations failed and Archadia's invasion of Dalmasca became total, placing the city of Rabanastre under Imperial control. Two years later, Gabranth and Vayne, then appointed consul of Rabanastre, arranged a banquet to celebrate Vayne's arrival, and Gabranth made sure the security forces of the palace were spotty. This too was a ploy, to draw the Resistance to attack, at which point the airship Ifrit and the Archadian forces outside the palace attacked to repel them. Coincidentally, Rek's brother Vaan had infiltrated the palace to steal that night, and flees during the attack. As he runs Vaan sees Gabranth and Vayne speaking. When Vaan is caught and brought before Vayne, he attempts to strike him but is blocked by Gabranth and thrown back before he can reach his target. Though Gabranth suggests Vayne show mercy as Vaan is not with the rebels, Vayne orders him executed and the two depart. Vaan mentions his brother was at the forces stationed at Nalbina Fortress, but at this time Vaan and Gabranth do not realize the deeper connection between them.

The night after the palace attack, Gabranth visits the Nalbina Dungeon where Basch is being held captive, and berates Ba'Gamnan, a bounty hunter searching for Balthier, a Sky Pirate captured along with Vaan and Fran. The three follow Gabranth to the chamber where Basch is held, where Gabranth interrogates him on the capture of Amalia, a member of the resistance who is actually Ashe using an alias. When Gabranth leaves Basch is freed by Vaan, Balthier and Fran, and the four escape the dungeon together. Still in Rabanastre, Gabranth tells Vayne that the imperial resistance in Bhujerba is suspiciously well-funded, and suspects Marquis Ondore to be behind them. Gabranth assists Vayne in searching the palace for the Dusk Shard for a period of time, but they are unaware it was stolen by Vaan before he fled the palace.
Drace and Gabranth discuss Larsa.

Some time after, Gabranth returns to Arcadia and reports Vayne's activities to Emperor Gramis, alerting him to Vayne's possible hand in the destruction of Nabudis through Judge Zecht, and his funding of Dr. Cid's experiments at Draklor Laboratory. Gramis worries he no longer knows Vayne's intentions and asks Gabranth to protect Larsa so that he does not become as brutal and merciless in his elder years as Vayne has. Judge Drace also confides in Gabranth that she fears for Larsa's safety due to the Imperial Senate desiring him an easily-manipulated heir over Vayne, and the two agree to defend him. After Gramis's death, Drace accuses Vayne of killing him, and she is subdued by Judge Bergan. Aware of Gabranth informing Gramis of his actions, Vayne appoints him as Drace's executioner as a test of loyalty. Reluctantly, he kills the Judge, but with her dying breath, she asks Gabranth to guard Larsa in her place, to which Gabranth promises that he would.

Later, Larsa urges Vayne to make peace with Ashe to avoid a war with the resistance, as the neighboring Rozarrian Empire would use this as a pretense to invade Archadia, beginning a second, much more destructive war with Dalmasca as the battleground. Believing Ashe wants a war, Vayne sends Gabranth to track her and ascertain her desires, and kill her if a war is indeed her intent. Atop the Pharos at Ridorana, Ashe approaches the Sun-Cryst, which she could use to cut shards of nethicite to use to fight the Empire. Gabranth emerges and urges her to do so, revealing he was the one who killed Raminas. Though enraged Ashe ultimately refuses the Cryst's power, realizing her vengeance will only lead Dalmasca to ruin. The dumbfounded Gabranth attacks them, but is defeated. Dr. Cid arrives, telling Gabranth that he is pitiful for failing Larsa and that he no longer serves any purpose, and when Gabranth attempts to strike the doctor Venat throws him back. The disgraced Judge Magister retreats unseen afterwards.

Cid's actions aboard the Sun-Cryst spill a powerful Mist over Ivalice, allowing Vayne to activate the Empire's most powerful weapon that until then lacked the needed magical energy - the Sky Fortress Bahamut, a massive airship. Aboard the Bahamut Gabranth again confronts the group, apparently still wounded and unable to understand how Basch has held onto his pride and honor despite repeated failures. Considering his disgrace the punishment he is due to aiding the Empire after they destroyed Landis, Gabranth attacks them again and is struck down, Basch urging him to reclaim his name and honor. The party leaves Gabranth to confront Vayne, who uses Cid's manufacted Nethicite to become Vayne Novus. Wounded and stumbling, Gabranth reaches the scene of the battle and raises his sword to Vayne, assisting the party in stopping him. As the battle ends Gabranth strikes Vayne with his empowered sword, but Vayne knocks him back with a powerful punch. As Gabranth lays in Basch's arms, Vayne summons his Sephira to finish him off but is stopped by Larsa, who uses his own nethicite to absorb his magic. Vaan then picks up Gabranth's fallen sword and strikes Vayne a second time, wounding him greatly and forcing him to retreat to the exterior of the Bahamut. In the subsequent battle Vayne and Venat merge into The Undying, and are destroyed together.
Basch takes up Gabranth's armor to serve as Larsa's protector.

With Vayne dead the party retreats to the Strahl to escape the falling Bahamut, and bring Gabranth aboard. With Larsa and Basch by his side, Gabranth asks Basch to protect Larsa in his stead, as the Arcadian Empire would fall into strife without House Solidor to lead them. Basch agrees, and Gabranth dies. Shortly afterwards, Basch impersonates Gabranth to announce a ceasefire to the Arcadian fleet, ordering them to withdraw. The masquerade persists as Basch takes up Gabranth's armor and accompanies Larsa back to Arcardia, serving as his bodyguard.