When Harry arrives at the Burrow in Harry Potter and the Goblet of Fire, Molly finds out about Fred and George's experimenting with dangerous sweets they were manufacturing and tells them off before leaving for the Quidditch World Cup; however, after the Dark Mark appears over the sky at the World Cup campsite, Molly is upset for yelling at Fred and George, worried that something might happen to them after she treated them so horribly. Later in the book, Molly believes the article that tabloid journalist Rita Skeeter writes about Hermione betraying her supposed "boyfriend" Harry, but when Harry tells Molly that this was a fabrication, she immediately warms up to Hermione. Molly and Bill arrive at Hogwarts to see the Third Task of the Triwizard Tournament, acting as family guests to Harry. After the return of Lord Voldemort, Dumbledore asks Molly and Bill to join the Order and fight in the impending Second War. Molly comforts Harry and, for the first time in his life, he has someone to be there for him, like a mother.
At the beginning of Harry Potter and the Deathly Hallows, Molly feels immensely uncomfortable with the trio's decision to drop out of Hogwarts, and initially attempts to dissuade them from doing so. While Bill and Fleur's wedding is taking place, the Ministry collapses and Death Eaters attack the wedding guests as the protection disappeared, prompting the trio to leave. The author later reveals that the Weasleys are safe; but, as the novel progresses, the family is forced to head for safety at Auntie Muriel's home. At the end of the book, Molly and her entire family fight in the Battle of Hogwarts. Upon seeing the death of Fred, she becomes devastated, and is pushed to the edge when Bellatrix Lestrange almost strikes Ginny with the Killing Curse. In great fury, she engages Bellatrix in an intense duel, killing her with a curse that hits Lestrange in the chest.