- Albus Dumbledore: "Severus, you wouldn't know anything about a Weasley being Sorted into Slytherin would you?"
- Severus Snape: "As I understand it, the Hat sorts based on personality and the traits of that individual. It seems to me young Bill is full of determination and ambition."
- — Albus Dumbledore discussing Bill's Sorting with Severus Snape
During school, Bill showed great ambition; he brewed good potions, was a brilliant Arithmancer and was at the top of his class in the Study of Ancient Runes. Bill was also talented in Defense Against the Dark Arts, however, like all Slytherins, he was met with disdain by Professor Montgomery, causing his grades in the course to fall until Montgomery's sacking in 1987 thanks to a combined effort of several Slytherin students backed by their head of house; Professor Snape. Bill and Professor Snape had a good mentor-student relationship; Snape gave Bill and a few of his fellow Slytherins private Defence lessons to combat Professor Montgomery's bigotry. Bill was made a prefect in his fifth year, and spent his sixth year taking part in a student exchange program with the Brazilian wizarding school Castelobruxo, where he finally met his Brazilian pen-pal; Gloria Silva. In his seventh year, he returned to Hogwarts with Gloria, who was also Sorted into Slytherin, and became Head Boy, graduating with top marks in his year.
After Hogwarts, Bill went on to work for Gringotts bank, eventually becoming a Curse Breaker for their Brazilian branch. In 1994, Bill mentored Harry Potter during a Curse Breaking expedition in Central America. When Wizarding Britain was once again thrust into war, Bill returned to England to fight in the war as a member of the Order of the Phoenix. During the Death Eaters' takeover of Hogwarts, Bill suffered injuries from Fenrir Greyback, which unfortunately turned him into a werewolf.