Karliah was trained in the art of thievery by her mother, Dralsi Indoril, and is the granddaughter of Queen Barenziah, as well as Drayven Indoril, who is rumored to be a descendant of the Dunmer saint Indoril Nerevar. She was a member of the Thieves Guild and the Nightingales along with Gallus Desidenius and Mercer Frey. She was also involved romantically with Gallus Desidenius, who called her his "Little Nightingale." She also stated that she owes her skills to Gallus saying "He honed my skill to a razor sharp point." Karliah was exiled from the guild for 25 years after Mercer framed her for Gallus' murder.
Karliah is the only Dunmer in the game whose eyes are 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. Parts of it can appear purplish in some light and it also appears to have a unique dagger strapped to the left shoulder, though it is for aesthetic purposes.
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, and 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, made to slow the victim's heartbeat and stop them from bleeding out, they survive. Karliah then takes them back to her camp outside the Sanctum to nurse them back to health. After the Dragonborn regains their strength, Karliah sends them to Winterhold to figure out how to decode Gallus's Encoded Journal.
The Dragonborn is sent to Calcelmo by Enthir to duplicate the writings on Calcelmo's Stone, in Calcelmo's Tower. He will not let them in, so the Dragonborn has to gain entry to the museum in another way. Once the translation is acquired, Karliah will be present at the Frozen Hearth inn with Enthir who will translate the passages, confirming that Mercer not only stole vast amounts of gold from the Guild but desecrated something called the "Twilight Sepulcher". Karliah will express utter shock at this but cannot elaborate just yet. With the evidence in hand, Karliah asks the Dragonborn to meet her in The Ragged Flagon to confront Mercer and reveal the truth to the Guild, awarding them with an item which once belonged to Gallus: a Nightingale Blade.
The Dragonborn meets Karliah and faces the Guild with her. Karliah hands over Gallus' journal as proof of her innocence and joins Brynjolf and the others as the vault is opened to reveal that Mercer robbed it dry. Though this vindicates her, she is just as angry as the rest of them and refers the Dragonborn to Brynjolf, who asks them to find evidence of Mercer Frey's whereabouts and will have to infiltrate his house to get his plans.
The Dragonborn learns about the Nightingales and is 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, The Dragonborn 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.
- Karliah was voiced by Moira Quirk.
- Her armor has a dagger strapped on next to the left shoulder.
- Unlike other Guild members, Karliah does not wear matching Thieves Guild Gloves or Boots. She instead uses unarmored boots and gloves.
- When asked about the Pilgrim's Path, she says, "It was said they would live forever in twilight," although the subtitles say, "They would become one with the shadows."
- During the quest "Speaking With Silence," if the Dragonborn uses the shout Aura Whisper she will not be detected by the shout like other NPCs are.
- Karliah, and both Sarethi sisters, Avrusa and Aduri, are the only Dunmer seen in Skyrim who do not possess their race's signature red eyes. (This potentially excludes the Dragonborn.)