Gryffindor wins the House Cup in "Harry Potter and the Philosopher's Stone" (also known as "The Sorcerer's Stone" in the US). The dramatic win comes at the end of the school year, thanks to last-minute points awarded by Professor Dumbledore to Harry, Hermione, Ron, and Neville for their bravery and actions in thwarting Voldemort's plan. This victory is a significant moment in the book, symbolizing the triumph of good over evil and the value of bravery and friendship.