Born in Hasselt, Belgium, Vaesen spent his first professional season at Belgian sides Cercle Brugge and K.S.C.
He was given the first-choice goalkeeper role at Birmingham, helping the club win promotion to the Premier League via the play-offs in 2002.
A memorable moment in the promotion season was saving a Gary Holt penalty in a 1–0 over Norwich City.
[2] Birmingham would go on to meet Norwich again in the play-off final and this time Vaesen saved from Philip Mulryne in the shootout.
[6] He finally dislodged Taylor in late 2005,[7] but a 4–1 defeat at Manchester City, in which he conceded a penalty and was later sent off,[8] proved to be his last first-team appearance before he was released at the end of the 2005–06 season due to Birmingham's relegation.