Justin Finch-Fletchley was a Muggle-born wizard and a student in Hufflepuff House at Hogwarts School of Witchcraft and Wizardry, in the same year as Harry Potter. Initially friendly, he grew fearful of Harry during their second year after witnessing him speak Parseltongue. Justin was one of the victims Petrified by Slytherin's Basilisk but was later cured. He eventually reconciled with Harry and joined Dumbledore's Army in their fifth year, demonstrating his loyalty in the fight against Lord Voldemort.
Justin first interacted with Harry Potter during a Herbology lesson in his second year, where he enthusiastically introduced himself. He revealed that he was Muggle-born and was originally set to attend Eton College before he received his Hogwarts letter. He expressed amazement at the Wizarding world and at having a celebrity like Harry in his class. His opinion of Harry changed drastically following a disastrous Duelling Club meeting. When Draco Malfoy conjured a snake, Harry spoke Parseltongue to stop it from attacking Justin. Unaware of Harry's intentions and knowing that Parseltongue was the mark of a Dark Wizard, Justin fled in terror, believing Harry had set the snake on him. His friend, Ernie Macmillan, later voiced the Hufflepuff theory that Harry was the Heir of Slytherin. Shortly after this incident, Justin was found Petrified in a corridor by Harry and Peeves. He had been attacked by the Basilisk, which he had seen through the transparent body of the Gryffindor house ghost, Nearly Headless Nick, who was Petrified alongside him. This fortuitous circumstance saved his life. Justin remained in the Hospital Wing for the remainder of the school year until he was revived by Professor Sprout's Mandrake Restorative Draught. In his fourth year, Justin was a staunch supporter of the Hogwarts Champion, Cedric Diggory, during the Triwizard Tournament. Like many Hufflepuffs, he was initially hostile towards Harry's controversial entry, wearing a “Support CEDRIC DIGGORY” badge that could be enchanted to read “POTTER STINKS.” By his fifth year, Justin's attitude had changed again. Convinced by Hermione Granger's arguments about the return of Lord Voldemort, he joined Dumbledore's Army to learn practical defensive magic from Harry. He attended meetings and trained alongside other members, showing his commitment to opposing Dolores Umbridge and the Ministry of Magic's suppressive regime. As a Muggle-born student, it is almost certain that Justin did not return to Hogwarts for his seventh year, as the Voldemort-controlled Ministry of Magic was actively persecuting and imprisoning Muggle-borns. His whereabouts during the Battle of Hogwarts are unknown.
Justin Finch-Fletchley is described in the books as having curly hair. His personality is initially cheerful, talkative, and perhaps slightly pompous, as evidenced by his casual mention of being on the list for Eton College. He can be easily influenced by public opinion and rumour, as seen in his fear of Harry and his support for Cedric Diggory. However, his decision to join Dumbledore's Army shows that he is ultimately brave and capable of forming his own judgments, aligning himself with what is right.
As a member of Dumbledore's Army, Justin received training in defensive magic from Harry Potter. He would have learned and practised a range of spells, including: