William was the second son of Philippe de Croÿ, Lord of Aarschot and Jacoba of Luxembourg. William married Maria-Magdalena of Hamal, widow of Adolf van der Marck. William bought the lordships of Beaumont and Chièvres from his father in 1485. In 1489 he was one of the lords who tried to reason with Philip of Cleves during his rebellion against Maximilian of Austria. William was also elected a Knight of the Golden Fleece in 1491. He became part of the court of Philip the Handsome in 1494, but did not accompany Philip on his first voyage to Spain in 1501–03. After Philip's death in 1506, William became part of the regency council and held chief responsibility for the finances of the Low Countries, as well as being supreme commander. He was confirmed in his tasks by Emperor Maximilian in 1510.