Olyvar is a spy and a prostitute, specializing in homosexual relations, in the employ of Petyr "Littlefinger" Baelish.
Olyvar poses as Loras Tyrell's squire during a sparring match. He makes flirtatious advances toward Loras and the two later have sex. Olyvar discovers that Loras is due to be married, and relays this information to Littlefinger shortly thereafter. Olyvar implies that noblemen in Loras' position make up the bulk of his clientele.
Olyvar has been left in charge of Littlefinger's brothels, presumably replacing Ros. When Oberyn Martell and Ellaria Sand arrive to King's Landing, they attend the brothel, with Olyvar showing three prostitutes to the couple. After Ellaria chooses one and dismisses the other two, Oberyn turns his attentions to Olyvar, who protests that he's not on offer before giving in and admitting he's just "wildly expensive". Oberyn asks if Olyvar has ever been with a prince before and orders him to remove his clothes, grabbing him by the crotch. However, they are interrupted when Oberyn overhears a pair of Lannister men singing "The Rains of Castamere".
Olyvar later takes part in a small orgy involving Oberyn and Ellaria. When the latter attempts to "share" him with Oberyn, Olyvar politely refuses her, claiming to have "not acquired the taste" for women. He then presses Oberyn to divulge his own preference. The Prince, however, explains his rather fluid approach to sexuality, a common trait among the Dornish. Olyvar and the other prostitutes depart when Tywin Lannister unexpectedly arrives to speak with Oberyn.
Olyvar continues to see Loras on a regular basis, though it's unclear if their arrangement is personal or professional. Around the time of Tywin Lannister's funeral, Olyvar is cuddling with Loras Tyrell post coitus, discussing the possibility of visiting Dorne or anywhere far away from King's Landing, when Margaery walks in. Staring down Olyvar, she admonishes Loras for making them late for supper with King Tommen, and tells Olyvar to leave.
Olyvar later plays the role of the Father with a fake beard when the High Septon visits the brothel, while a collection of female prostitutes play the rest of the Seven. He breaks character to make a snide remark about the High Septon's choice, and to remind him that two prostitutes will cost him extra. Moments later, the brothel is attacked by Sparrows, led by Lancel Lannister, who seize the High Septon. Olyvar attempts to tell them that they will have to answer to Baelish, but they strike him across the face and remove his fake beard.
Olyvar is present when the brothel is attacked again by the Sparrows, this time having formed into the Faith Militant with Cersei Lannister's permission. Again, he is struck when he tells them they will have to answer to Baelish, but this time, the Faith Militant have targeted the brothel's homosexual patrons and prostitutes who have been caught in the act. Since Olyvar is fully clothed, he is not suspected of homosexuality, and is able to flee the brothel when he sees the Sparrows castrate both the homosexual patron and the prostitute.
Olyvar is later called to give evidence at the "Holy Inquest" of Loras, who is accused of "fornication", "buggery", and "blasphemy", though it is clear he is doing it on Cersei's instructions. Despite their previous, affectionate relationship, Olyvar turns on his lover, and provides the High Sparrow with testimony that allows him to pursue formal charges against Loras. For his cooperation, Olyvar is spared from punishment for his own homosexuality.
One of Littlefinger's protégés, it was Olyvar who seduced Loras Tyrell and discovered the plot to marry Loras to Sansa Stark. Olyvar further betrayed the Tyrells when he testified to having intimate relations with Loras, a confession that landed two Tyrells in jail - loras for his "unnatural acts" and Margaery for bearing false witness before the gods.