A rather successful midfielder, Bosz started his professional career played with Vitesse in 1981; after a loan season with then-amateurs AGOVV Apeldoorn in 1984, he returned into professional football with RKC Waalwijk (from 1985 to 1988), then moving to France with SC Toulon (1988 to 1991), and successively playing six seasons with Dutch giants Feyenoord (1991 to 1996), Japanese club JEF United Ichihara (1996–97), German club Hansa Rostock (1997–98), NAC Breda (1998–99). He retired at the end of the year 1999 after a second spell with JEF United Ichihara.
After his retirement, Bosz started a managing career, becoming first head coach of amateurs AGOVV Apeldoorn, a position he held from January 2000 to 2002; in 2002 he also won a national amateur league title. He then made his move into professional football, becoming head coach of De Graafschap (2002–2003) and Heracles Almelo (2004–2006), also winning an Eerste Divisie title in 2005.
In July 2006, Bosz accepted an offer as technical director at his former club Feyenoord. He left the position on 14 January 2009 due to his opposition to the dismissal of head coach Gertjan Verbeek.
In the summer of 2010, Bosz started his second spell as manager of Heracles Almelo, replacing Verbeek who had moved to AZ Alkmaar in the meantime.