He is one of the prisoners at Harrenhal left for dead by Ser Gregor Clegane.
Qyburn is a former maester of the Citadel. He was stripped of his chain by the Archmaesters for engaging in forbidden experiments.
Qyburn is among the Northern and Riverlands prisoners at Harrenhal when Ser Gregor Clegane abandons the castle and has all captives put to the sword. Qyburn, however, survives the injury at his throat and awakens when the castle is taken by the Northern army. After he wakes, he identifies himself to Robb Stark while Talisa Stark tends to his wound.
After Robb Stark left Harrenhal, Qyburn stayed behind serving under Lord Roose Bolton. He tended to Ser Jaime Lannister's badly infected stump. During this Jaime notices that Qyburn is not a Maester, because he isn't wearing a maester's chain of office. Qyburn acknowledges this, explaining that he was stripped of his chain by the Citadel and thrown out of the Order of Maesters for conducting experiments which they felt were too "bold".
Qyburn volunteers to join the party escorting Jaime back to King's Landing. Lord Bolton theorizes that the former Maester is doing so in the hopes that Tywin Lannister will force the Citadel to restore his chain. After leaving Harrenhal, Qyburn informs Jaime that the Citadel removed his maester's chain for performing experiments on living humans in order to learn more about their anatomy. He justifies this by noting that he used the information he gleaned from them to save lives. When Jaime then asks Qyburn about Brienne, he states that her father offered Locke a fair ransom of three hundred Gold Dragons, which Locke refused to accept due to a previous lie of Jaime's that Brienne came from a wealthier family than she really did. Qyburn tells Jaime that she will most likely serve as entertainment for Locke and his men that night, and be killed thereafter. Qyburn then accompanies Jaime and Steelshanks to Harrenhal when Jaime blackmails Steelshanks into helping him rescue Brienne.
Qyburn is still with Jaime and Brienne when the two arrive at King's Landing.
Qyburn assists with the fitting of Jaime's new golden hand, at Cersei's request, and ingratiates himself with the Queen by aiding her in other matters.
After Gregor Clegane is seriously wounded during his fight against Oberyn Martell, Qyburn and Maester Pycelle theorize that Oberyn coated his spear in Manticore venom, causing Clegane's wounds to fester and leave him in agony. Pycelle advises Cersei that Clegane is doomed, but Qyburn opines that he may be able to save him using more unorthodox means. Pycelle snorts that Qyburn is not even a Maester, and reminds Cersei that he was expelled from the Citadel for conducting "dangerous" and "unnatural" experiments. Cersei responds by dismissing Pycelle from his duties - and his laboratory. Qyburn warns the Queen that the process he intends to put Ser Gregor through may "change him", but when she is satisfied that it will not affect his strength, she instructs Qyburn to carry on.
Qyburn is at Cersei's side when she confirms that a head brought to her by two bounty hunters does not belong to Tyrion Lannister. Qyburn asks for the head for use in his research. Later on, at a meeting of the Small Council, Cersei appoints Qyburn as the new Master of Whisperers to replace Varys. Grand Maester Pycelle protests vehemently given Qyburn's outcast status, and Kevan Lannister denounces Qyburn as a sycophant and Cersei as a power-grabber
Qyburn is present at a Small Council meeting when the High Septon demands the execution of the High Sparrow after his followers attack him. Qyburn informs the Council that the High Septon had been at Littlefinger's brothel. Later, Qyburn kills a rat as part of an experiment when Cersei enters his laboratory, giving him a message that she wants sent to Petyr Baelish. She also asks him about the state of his work, while glancing at Gregor Clegane's covered body, and Qyburn assures her it is going very well, though there is still a way to go. Soon after Cersei leaves, as Qyburn writes, Gregor begins shaking under the blanket, but Qyburn shushes him calmly
Qyburn is at the meeting of the Small Council when Mace Tyrell departs to negotiate the crown's debt with the Iron Bank of Braavos
Qyburn visits Cersei while she is held prisoner by the High Sparrow, informing her that Grand Maester Pycelle has sent for Kevan Lannister to serve as Hand of the King. He also informs her that King Tommen has become despondent following Cersei's arrest, and that he refuses to eat or see anyone. Finally, just before leaving her, he informs her that "the work continues," presumably referring to his experiments on Ser Gregor Clegane.
After Cersei enters the Red Keep following her walk of atonement, he hastily throws a cloak over her naked body after rushing to her side. He then speaks to Cersei softy and reassuringly as he embraces her, attempting to soothe her. Pycelle looks upon the scene with disgust. Qyburn remarks upon her poor state and bleeding feet. Qyburn then introduces the "newest member of the kingsguard," the 7-8 foot tall abomination he has been working on. At his behest, the golden knight picks her up and they walk away together, further into the Red Keep so Qyburn can clean her up and treat her wounds.
In his laboratory, Qyburn continues to serve as Master of Whisperers by bribing a group of Varys' little birds into his service with boxes of sweets. When Jamie and Cersei arrive accompanied by Gregor Clegane, the children are unnerved by the Mountain, though Qyburn promises them Clegane is a friend. As part of her revenge, Cersei asks Qyburn to bribe more of Varys' spies stationed in the other kingdoms, and he agrees to do so.
Qyburn enters Cersei's chamber to inform her that the Faith Militant have entered the Red Keep. Accompanied by Qyburn and the Mountain, Cersei confronts the group. Lancel says she must be taken to the High Sparrow, however Cersei disregards what her cousin is saying. Qyburn then watches as Gregor kills one of the sparrows. Later, Cersei, Qyburn and Ser Gregor enter the Great Hall to find a large crowd gathered for a royal announcement, King Tommen then announces that Cersei and Loras Tyrell's trial will be held in the sept of Baelor on the first day of the festival of The Mother then declares that Trial by combat is now forbidden. After the announcement Qyburn tells a shocked Cersei, who had been planning on calling a trial by combat with Gregor as her champion, that his little birds have been investigating an old rumor that she had told him about, and that the rumor was found to be much more than a rumor.
The rumor turns out to be the Wildfire plot, in which King Aerys II stored caches of wildfire across the city, including under the Great Sept of Baelor. Qyburn has his spies create leaks in the barrels containing the wildfire, then has them place candles in the middle of the resulting puddles, which slowly burn towards the wildfire. The wildfire ignites and destroys the Sept of Baelor, killing the High Sparrow, Mace Tyrell, Queen Margaery, Loras Tyrell, Kevan Lannister, and many others. Qyburn also has Pycelle assassinated by his spies so as to consolidate Cersei's power. For his service and loyalty, Qyburn is made Cersei's Hand of the Queen, and later crowns her as Queen of the Seven Kingdoms.
Qyburn is present when Cersei holds court with Euron Greyjoy. Qyburn also attends court with Cersei when she addresses the lords of the Reach, sworn to House Tyrell, to convince them to betray Lady Olenna for Cersei. When Lord Randyll Tarly asks about how Cersei is going to deal with Daenerys Targaryen's dragons, Qyburn tells the lords that he has been working on something. He later takes Cersei down beneath the Red Keep to show her his new weapon to kill one of Daenerys's dragons, inviting her to test it in the skull of Balerion, the dragon Aegon the Conqueror used to unite the Seven Kingdoms, and forge the Iron Throne.
Qyburn and Ser Gregor are present in the dungeons when Cersei confronts Ellaria Sand and her daughter Tyene Sand, who had murdered her daughter Myrcella Baratheon. Cersei tells Ellaria and Tyene that Qyburn managed to ascertain that they had poisoned her daughter with the Long farewell. Cersei kisses Tyene with the Long farewell and Qyburn gives her the antidote. Qyburn and the others then leave a distraught Ellaria to mourn with her dying daughter.
When Tycho Nestoris meets again with Cersei Lannister, the Queen assures the representative of the Iron Bank of Braavos that the bank will soon have its gold. Tycho suggests that the Iron Bank may invest in Cersei in her venture to establish her control over the Seven Kingdoms of Westeros, and Cersei informs Tycho that her her Hand has already reached out to the Golden Company, a powerful sellsword company in Essos.
Qyburn's scorpion is used in Battle of the Goldroad, when Bronn fires it into Drogon's shoulder. It succeeds at injuring Drogon enough to make him land. Out of anger, the dragon later destroys the weapon.
Upon Jaime's return to King's Landing and his meeting with Tyrion, Qyburn reveals to Cersei that she is pregnant. She dismisses him after Jaime walks into the room, allowing Cersei to reveal the good news to her brother in private.
Qyburn is present at the meeting at the Dragonpit, which he helped Cersei organize. He comes forward after Sandor begins cutting up the wight presented for Cersei, reaching for the wight's severed arm, and examining it with genuine curiosity, although even he seems somewhat unnerved by it. He gives the hand to Jon Snow, who demonstrates burning the hand.
Qyburn studied to be a maester but wears no chain because the Citadel expelled him fot unauthorized experiments. intrigued by his abilities, Queen Cersei gave him Pycelle's lab and, after Vary's disappearance, named him Master of Whisperers. During Cersei's imprisonment, Qyburn remained faithful to the Queen Mother and helped her execute her plan to destroy the Sept of Baelor. For his loyalty, the new queen appointed him as her Hand.
Externally, Qyburn appears to be an extremely harmless, polite and serene old man - he behaves calmly and patiently around everyone he meets, even if they do not have a good impression of him. Jaime viewed him as an "odd little man" and didn't entirely trust him, even when Qyburn operated on the wound left by his severed hand. Qyburn has proven himself to be, in his own right, highly intelligent to a fault, so much that he was the only one who knew a way to save Ser Gregor Clegane after he was savagely wounded by Oberyn Martell during their fateful duel in the trial by combat. When Qyburn expressed that he knew a way of saving Gregor, he did so without bragging, instead that it was a matter of fact, which Pycelle interpreted as arrogance and pride. Qyburn is, at the same time, extremely secretive, not truly revealing the methods he used to save the Mountain, instead expressing that the process would change Gregor, but not weaken him, and make him supremely obedient to Cersei. Qyburn doesn't seem to express any outward disdain towards Ser Gregor for almost killing him at Harrenhall, but then again Qyburn rarely expresses disdain for much of anything. It is therefore unknown whether Qyburn suggested he experiment on Ser Gregor out of revenge or if he simply did so in the interest of his constant pursuit of knowledge.
In spite of Qyburn's soft and calm exterior, he is potentially a very dangerous man because of his secretive, ruthless and unethical methods. The Citadel once expelled Qyburn on the basis that the experiments that he enacted were unnatural and unacceptable, which Qyburn deemed foolish. Pycelle scorns Qyburn for this, naming him an embarrassment to the Citadel. Qyburn maintained his loyalty to Cersei and carried out any task she set for him, but it is unspecified if he had personal reasons or if he was simply loyal to Cersei. Qyburn was quick to end the interference of Pycelle in Cersei's plots by having him assassinated by his little birds. In spite of this, Qyburn expressed that he himself didn't have any personal grievances towards Pycelle and even told the old man that the necessity of murdering him pained Qyburn - this shows that Qyburn does not have sadistic or murderous intentions, but simply saw the act of killing the old Grand Maester as utterly necessary to consolidate Cersei's power. However, none of these factors prevented Qyburn from having a look of cold satisfaction on his face as he watched his little birds overwhelm Pycelle.