Born in 1965 in Schriek, near Heist-op-den Berg (Belgium), Koen Nys started studying music at the local music academy at the age of 14, also thanks to the support and encouragement of his brother. He developed a genuine passion for jazz attending international concerts at the "Hnita Hoeve". In 1985 he started studying at the then newly created Jazz Studio, in Antwerp (Belgium), for two years, where he attended private classes by John Ruocco. His fellow students were Erwin Vann, Hendrik Braeckman, Piet Verbist, Frank Vaganee and others. He also took part in the Jazz Workshops in Dworp and attended classes by Joe Lovano.

​Koen left Belgium and headed for Montréal in 1987 where he studied at the McGill University and obtained the degree in "Jazz Performance". After his studies at the McGill University he played with various bands in Montréal. Koen performed with his own quintet at "Le festival International de Jazz de Montréal". One year later he exchanged Montréal for Tokyo, Japan, where he resided for two years, both performing with various bands and teaching. In the summer of 1995, he participated in the Jazz Workshop in Banff, Canada, and had the opportunity at this venue to work together with Kenny Wheeler and Joe Labarbera. Afterwards, Koen moved to New York (US), where he studied with George Garzone and fully enjoyed the New York Jazz Scene. He toured with local musicians and recorded his first CD entitled ‘CHIMBE'. ​

He briefly returned to Montréal; performed at several ‘hotel-gigs' in the Arabic Emirates and Korea and finally settled again in Belgium. Back home he performed several times with "The Brussels Jazz Orchestra" and worked together with – amongst others - Dré Pallemaerts, Felix Simtaine, Free De Smijter, Kurt Van Herck, Lieven Venken and Piet Verbist performing in jazz clubs mostly in Antwerp and Brussels. As from October 2001, Koen teaches at the Jazz Studio in Antwerp and at several music academies in Belgium (Tongeren, Heist-op-den-Berg and Lennik). In 2003, Koen was invited as guest musician for the debut CD of Chris Mentens, ‘Jazz Van'. He was part of the hip band ‘Milleniums', recording their first CD in 2003, followed by the second one in 2009. He performed with his own quartet or as a freelance musicians in clubs, in the company of –amongst others - Bram Weijters, Marek Patrman, Manolo Cabras, Ewout Pierreux,