Czekaj, 28, has made 141 appearances for Blues - scoring 26 tries - over the last decade and will add to that total when he starts tonight's RaboDirect PRO12 game with Edinburgh Rugby at Meggetland.
The Cardiff-born wing/full back made his Wales debut against Canada in 2005 and made his Six Nations debut against Ireland in 2007.
Czekaj currently stands ninth in the all-time Blues appearance maker charts (141 games) and fifth in the try scoring history rankings (26 tries in all competitions).
He said: "My association with Cardiff Blues and Cardiff RFC goes back over the last decade and I've had a fantastic career with the Blues since making my Celtic League debut back in 2004.
"I've made many lifetime friends over the years and will leave with many happy memories, with one of the obvious highlights being the Amlin Challenge Cup victory in 2010.
"I would like to thank all the players I have been fortunate to play with over the years, the coaches at the Blues and also the fantastic supporters we have who have always backed me.
"I will continue to give Cardiff Blues 100 per cent until the end of this season before I start a new challenge and chapter of my life that I am excited about in France with Colomiers."
Peter Thomas, Chairman at Cardiff Blues, added: "Chris has been a magnificent servant for the region over a decade and a real role model to young players coming through the ranks to aspire towards. He has been a key performer for the Blues and we thank him for his service.
"Everyone connected to the Blues now wishes him and his family every success for the future and the next part of his rugby career in France."