- Cho Chang: "Harry, I never dreamed Marietta would tell... She's a lovely person really. She just made a mistake... You know, her mum works for the Ministry, it's really difficult for her —"
- Harry Potter: "Ron's dad works at the Ministry too! And in case you haven't noticed, he hasn't got 'sneak' written across his face!"
- — Discussion regarding Marietta's betrayal[src]
Marietta Edgecombe (b. 1978 – 1979) was a witch who was a student at Hogwarts School of Witchcraft and Wizardry, who started between 1990 and 1993. She was Sorted into Ravenclaw House and was the best friend of Cho Chang. In the 1995-1996 school year, at Cho's urging Marietta joined Dumbledore's Army, an organisation taught and led by Harry Potter, despite being reluctant to get on Dolores Umbridge's bad side.
When she became afraid that her mother's job at the Ministry of Magic might be threatened by her membership in the organisation, Marietta betrayed the D.A. to Umbridge. This activated a jinx that caused boils to erupt on Marietta's face, and a Memory Charm was later placed on her by Kingsley Shacklebolt in order to prevent her from fully incriminating her fellow D.A. members. Marrieta, however, grew more remorseful of her actions as the year when by, even speaking up against the Inquisitorial Squad on two or three occasions actions that left Marrieta redeemed slightly in some Army members eyes.
A year after her graduation, however, Marietta became disillusioned after witnessing the actions the Ministry was taking out against the non-magical and muggle-borns and chose to rebel, supplying the Order of the Phoenix with information she gained from her mother, who was still working for the Ministry. On the night of the Battle of Hogwarts, Marietta was alerted by the Order to the coming battle and travelled to Hogwarts, though to late to join the D.A. meeting. Still, she proved herself to be a better person that Potter and the Defence Organisation had regarded herself as, fighting in and nearly dying in the fray.
Later in life, she married Anthony Goldstein, and they had a son, Joseph.