Percy Ignatius Weasley is the third son of Arthur and Molly Weasley. When readers first meet Percy in Harry Potter and the Philosopher's Stone, he is a Gryffindor prefect, and in Harry Potter and the Prisoner of Azkaban, he becomes Head Boy. In Harry Potter and the Chamber of Secrets, Percy secretly has a girlfriend — Ravenclaw prefect Penelope Clearwater. Academically a high-performing student, Percy received twelve OWLs. When he finished school, this academic distinction secured him a job in the Ministry of Magic in Harry Potter and the Goblet of Fire. His immediate employer is Barty Crouch Sr, the Head of the Department of International Magical Cooperation; Percy somewhat idolises Mr Crouch, but Crouch never seems to remember Percy's name, calling him "Weatherby." When Crouch is ill, Percy replaces him as a judge in the second Triwizard Tournament task. He is also scheduled to be a judge for the final task, but is forced to attend an inquiry regarding Crouch's mysterious long absence.

In Harry Potter and the Order of the Phoenix, Percy is promoted to Junior Assistant to the Minister Cornelius Fudge; because Fudge and Dumbledore are at odds over Harry's claim that Voldemort returned, a dispute between Percy and Arthur erupts, resulting in Percy's subsequent alienation from his family. When Percy learned Ron is made a prefect, he sends him a letter congratulating him for following in his footsteps, and unsuccessfully urges Ron to sever ties with Harry (claiming Harry is an extreme danger to Ron's prefect status), and to pay loyalty to the Ministry and Dolores Umbridge. Percy later makes an appearance in Harry Potter and the Half-Blood Prince, where he has apparently seen the error of his ways and pays a visit to his family with new Minister for Magic Rufus Scrimgeour during the Christmas Holidays, although it is later revealed that this is a mere opportunity for Scrimgeour to speak to Harry alone.

In the climax of Harry Potter and the Deathly Hallows, Percy returns to his family and manages to make up with all of them, and eventually duels new Minister for Magic and Voldemort's puppet Pius Thicknesse in the Battle of Hogwarts. Halfway through dueling alongside Percy, Fred is killed in an explosion, and Percy clings to the corpse and shields it from further damage. Then, Percy sprints off to pursue Augustus Rookwood, a Death Eater whom he believes killed Fred and who is then attacking an unnamed group of students. In the last part of the battle, he and his dad work together to floor Thicknesse. His final appearance is in the book's epilogue, at King's Cross Station, talking loudly about broom regulations