Born in Purmerend in the province of North Holland in 2008, Sean began his footballing career at RKAV Volendam, joining the club as a six-year-old. Two years later, Sean moved to Ajax's famous youth academy.
During the 2024/25 season, he began training with the first team before making his Eredivisie debut in February 2025, appearing in the closing stages of a 4-0 win against Heracles Almelo.
Sean's development continued into the following season as the teenage Dutchman enjoyed a breakthrough campaign at senior level last term after making 25 appearances, including 18 starts.
Upon arriving at Newcastle, Steur said: “I was at home at Ajax – I joined when I was seven and I leave with only good memories, but when a club like Newcastle comes for you, it’s really hard to say no. The last few days have gone fast and I’m very happy to join."
