Season 3

After learning the abuses Sansa Stark suffered at the hands of Joffrey, Olenna realised that Margaery could avoid the same fate by using Joffrey's love of violence. Varys warns Olenna that Petyr Baelish has designs on Sansa, who, given the death or disappearance of all her brothers, is now the key to the North. Olenna thus secretly plots to have Sansa marry Loras.^[11] Her plan is foiled by Loras, who accidentally reveals it to his new lover, one of Baelish's spies. Baelish informs Tywin Lannister, who has Sansa marry his son Tyrion Lannister instead. To secure the Reach, Tywin orders his daughter Cersei to marry Loras. Lady Olenna is at first against this because Cersei is too old (and therefore unlikely to have more children) and because of the scandal of her incestuous affair with her twin brother Jaime. After Tywin threatens to make Loras join the celibate Kingsguard, which would make Joffrey and Margaery's children the heirs of Reach, Olenna admits defeat and praises Tywin for getting the best of her.

Later, Tyrion, as Master of Coin, meets with Olenna to discuss the enormous cost of Joffrey and Margaery's wedding, hoping to get her to agree to scale back the plans she helped make for the event. Olenna reminds Tyrion that a royal wedding can distract the smallfolk from their discontent and is therefore worth the cost. She does, however, agree to have House Tyrell pay half the expenses for the wedding so the event can go on as planned.

Season 4

Olenna conspires with Petyr Baelish to murder Joffrey, so as to protect Margaery from Joffrey's beastly nature – it is Olenna who actually does the deed, using a poison Petyr arranged to have smuggled into the wedding on Sansa's person. Quietly admitting her actions, Olenna advises Margaery to become acquainted with her new match, Tommen Baratheon, Joffrey's younger brother and heir, before Cersei turns him against her. Olenna returns to Highgarden shortly afterwards.

Season 5

When Loras is arrested by the recently reinstated Faith Militant for his homosexuality, Margaery writes to her grandmother who returns to the capital to protect her grandchildren from Cersei's schemes. Mistakenly believing Loras's arrest was simply meant to humiliate House Tyrell, she helplessly assists Olyvar's testimony which incriminates her grandson, as well as to Margaery's incarceration for perjury in front of the gods to protect her brother. She later confronts the High Sparrow without result and has a secret meeting with Littlefinger who, blackmailed by Olenna for his part in Joffrey's death and to atone for his role in her grandchildren's imprisonment in providing Olyvar to Cersei, gives valuable information about Lancel and Cersei's adulterous relationship. This results in the latter's arrest by the Faith Militant.

Season 6

Olenna takes steps to free Margaery from the High Sparrow and retake power from the Faith Militant but is thwarted when Tommen forges an alliance with the Faith and becomes the High Sparrow's new puppet. Margaery feigns loyalty and manages to instruct Olenna to leave the city when the High Sparrow threatens her life. Cersei's plotting ultimately causes the destruction of the Great Sept of Baelor, killing Margaery, Loras, Mace and the High Sparrow. A grieving Olenna is invited to Dorne to meet with Ellaria Sand, who has seized control of the region and rebelled against the Lannisters. In Dorne, Ellaria presents Varys, who persuades Olenna to support Daenerys Targaryen, having been a secret Targaryen loyalist all along. Olenna sends the Tyrell fleet to Meereen to assist in taking Daenerys' forces to Westeros.^[12]

Season 7

During a meeting with Daenerys' allies at Dragonstone, Olenna shows her doubts about Tyrion Lannister's plan to attack King's Landing using the Tyrell and Dornish forces but eventually agrees. After the meeting, Daenerys asks Olenna to stay to talk with her. Daenerys acknowledges that Olenna has joined forces with her to exact revenge for her family and not out of any loyalty to her. Olenna advises Daenerys not to listen to "wise men" such as Tyrion, as that is how she has stayed alive all these years. She then tells her the lords of Westeros are all sheep and Daenerys is a dragon, so she should be a dragon. In "The Queen's Justice", Jaime Lannister seizes control of Highgarden on Cersei's orders. He confronts Olenna, granting her a painless death by poison, putting it in her cup of wine as she watches. She drinks the cup all at once and then admits her responsibility for Joffrey's death, wanting Cersei to know who had done it.

Recognition and awards

Diana Rigg received positive reviews for her role as Olenna Tyrell in the TV series.^[13][14] Screen Rant called Rigg's performance full of energy and fun, saying that the character is "refreshing" and has "sassy put-downs and blunt talk, she is likely the closest thing to comic relief we have in the show."^[15]

For her performance in the series, she received Primetime Emmy Awards nominations for Outstanding Guest Actress in a Drama Series in 2013, 2014, 2015 and 2018,^[16][17][18] and Critics' Choice Television Award nominations for Best Guest Performer in a Drama Series in 2013 and 2014.^[19][20]