Myrcella Baratheon is a fictional character in the A Song of Ice and Fire series of epic fantasy novels by American author George R. R. Martin, and its television adaptation Game of Thrones. Myrcella's character, development and her interactions and impact differ greatly between the two media.

Introduced in 1996's A Game of Thrones, Myrcella is the only daughter of Cersei Lannister from the kingdom of Westeros. She subsequently appeared in Martin's A Clash of Kings (1998) and A Feast for Crows (2005).

Myrcella is portrayed by Irish actress Aimee Richardson in the first two seasons of the HBO television adaptation, while English actress Nell Tiger Free portrays her in the show's fifth and sixth seasons.

Since Myrcella Baratheon is not a point of view character in A Song of Ice and Fire, the reader learns about her through other characters' perspectives, such as her uncle Tyrion Lannister. She is a background character in the books.

Myrcella is introduced in A Game of Thrones (1996) as the only daughter of Queen Cersei Lannister and King Robert Baratheon. In her first appearance, she accompanies her parents, her two brothers (Joffrey and Tommen Baratheon), her uncle Tyrion and her "uncle" Jaime Lannister to Winterfell, where Robert asks Eddard Stark to be appointed as Hand of the King. She is later shown attending the tournament to celebrate Eddard's inauguration into his position. While investigating Jon Arryn's death, Eddard discovers that Myrcella and her brothers are the products of an incestuous affair between Cersei and Jaime.

In 1998's A Clash of Kings, Myrcella attends Joffrey's nameday as King. She greets her uncle Tyrion and tells him that she is glad that the rumors of his death were false. During the War of the Five Kings, Tyrion makes plans to forge an alliance with House Martell of Dorne by having Myrcella wed to Trystane Martell, the youngest son of the current ruler of Dorne, Doran Martell, but part of the arrangement involved sending her to Dorne to live in the Martell household.

During A Storm of Swords (2000), Trystane's sister Arianne Martell plans to crown Myrcella as Robert's heir instead of Tommen, hoping to incite the Dornishmen to rebel against the Lannisters to seat her on the Iron Throne. However, Doran Martell has been tipped off to the conspiracy and his men ambush Arianne's party as they attempt to sail up the Greenblood. In the ensuing confrontation, one of Arianne's co-conspirators, Ser Gerold "Darkstar" Dayne, attempts to kill Myrcella; although unsuccessful, he cuts off one of her ears and leaves her scarred.

In A Dance with Dragons (2011), Myrcella travels back to King's Landing with Nymeria Sand.