Harry Potter was killed when Bill was eleven. His entire family went on the run, his mother taking the four youngest and his father taking him, Charlie and Percy. Just before Bill turned sixteen, Arthur moved him and Charlie to Scotland, leaving Percy temporarily with their mother, but Snatchers came and dragged Bill away from his family. They tried to take Charlie too, but Arthur managed to save his younger son and go deeper into hiding. Bill was taken to the Slytherin Academy with no idea what had happened to his family.
He attended the Academy as a servant for the required five years, after which he was sent to the Northumberland Labour Camp. It was here that he learned that while Charlie was still safe, his younger brother Percy had given himself up and was now a student at the school, and several years later, that Ginny had been captured and was now also a servant.
When he found out about Ginny, Bill used what little power he had to help get an unpaid position as Groundskeeper at the Academy. Returning there, he was reunited with Ginny and, later, his brother Ron. He also met Fleur Delacour, the Professor of Etiquette, and began a romantic relationship with her. She eventually became pregnant with his child, but he is unable to publically acknowledge his offspring due to his blood traitor status. He was responsible for the Weasley and Longbottom families becoming aware of the relationship between his sister Ginny and Neville Longbottom.