She was trained in the art of thievery by her mother, Dralsi Indoril, and is a descendant of Drayven Indoril, who was rumored to be a descendant of the Dunmer saint Indoril Nerevar. She was also involved romantically with Gallus Desidenius, who called her "My Little Nightingale." A former partner in the Thieves Guild with Mercer Frey, Karliah was exiled from the guild for 25 years after he framed her for Gallus' murder.
As a descendent of Queen Barenziah, her mother may have been the illegitimate child of Tiber Septim named Dralsi Indoril, in turn making Karliah a possible Septim and giving her a claim to the Cyrodilic throne as Empress.
She is the only Dunmer in the game whose eyes are not red (instead violet). Her armor is a lighter shade of gray than the Guild Master's Armor Set, and has the same brown-colored straps and satchels of the Thieves Guild Armor.
Once Mercer picks the Dragon Claw door, the Dragonborn walks in first. Karliah shoots the Dragonborn with a poisoned arrow, and the Dragonborn passes out soon after. Awakening again, their vision is blurry. Mercer and Karliah are heard talking. From their dialogue, it is learned that Mercer is guilty of committing many crimes against the Guild. Karliah escapes and Mercer notices the Dragonborn is still alive.
He stabs the Dragonborn, attempting to kill them, but because of the poison on Karliah's arrow, which slowed the Dragonborn's heartbeat and stopped him/her from bleeding out, he/she survives. Karliah then takes the Dragonborn back to her camp outside the Sanctum to nurse them. After the Dragonborn regains their strength, the two head to Winterhold to figure out how to decode Gallus' journal.
The Dragonborn is sent to Calcelmo by Enthir to duplicate the writings on the Calcelmo's Stone in Calcelmo's Tower. Calcemo will not let them in so they have to gain entry to his museum in another way.
The Dragonborn learns about the Nightingales and are taken to the Nightingale Hall by Karliah and Brynjolf to become a Nightingale. She wants them to be prepared for the task of killing Mercer Frey for his betrayal.
Karliah and Brynjolf have traveled to Irkngthand in their pursuit of Mercer Frey. They want the Dragonborn to meet them there. Inside they need to locate and eliminate Mercer and take the Skeleton Key he has stolen from Nocturnal.
The Dragonborn must return the Skeleton Key and in order to do so they have to follow the Pilgrim's Path inside the Twilight Sepulcher. After this is done they can go back to the cave and choose a power each day.
- When Karliah appears to teleport or disappear in her confrontation with Mercer, she actually drinks an invisibility potion. It is possible to witness her disguised form leaving.
- Her armour has a dagger strapped on next to the left shoulder.
- She is the only Dunmer in the entire game not to have red eyes.