He studied fashion at the Rijn IJssel College in Arnhem where he graduated in 1997. Then he studied Fashion Design at the AKI Academy of Fine Arts in Enschede until his graduation in 2001.
In 2005 he established the Bas Kosters Studio in Amsterdam. In 2003 he got his Masters Degree at the Fashion Institute Arnhem, his graduation collection earned him the Robijn Fashion Award. In 2004 Bas Kosters designed a stroller for Bugaboo International, the collaboration was repeated in 2011.
In 2005 he established Bas Kosters Studio.
Since 2006 he regularly presents new collections, both during Amsterdam Fashion Week, and the London Fashion Week, like his collection The Munchies. In 2012 he presents the collection "That puts the "U’ in Ugly", that includes the "penis pants" a legging with a print of penises.
This item (officially called "Is that a cock or your legs") gets a lot of international attention. Bas Kosters is fascinated by clowns and even dedicated a collection to them: Clowns Are People Too.
Since 2007 Bas Kosters has been organizing the twice a year.
lieutenant"s meant as a counterpart of the "glamorous" Amsterdam Fashion Week".