In March 1999 Koen Kessels founded the Hermes Ensemble, specialising in 20th and 21st century music. He debuted as a conductor with the Vlopera orchestra in Cinderella by Prokofjev, a production of the Royal Ballet of Flanders, an organisation for which he subsequently conducted several productions. As an opera conductor he was in high demand in Flanders and in 2005 he debuted at the Paris Opera where he took on three of the seven productions during the following seasons.
Koen Kessels was a guest conductor at the National Opera of Sofia, music director of the Summer Opera Festival Alden Biesen, creative director of the Hermes Ensemble and member of the artistic management of the Conservatory of Antwerp responsible for singing, strings and management departments and creative productions. He also sees to the coaching of the vocal repertoire. As of the 2010-2011 season he became the music director of the Birmingham Royal Ballet for a five year period and has been a host conductor of the The Royal Ballet Opera House Covent Garden since 2008.