The 25-year-old believes the switch is the right decision at this stage of his career - but acknowledges leaving the Arms Park after seven years will be tough.
"I'll be incredibly sad to say goodbye to everyone at the Cardiff Blues, the fans, the squad and the staff," he said.
"I've been very fortunate to have spent the last seven years there with great players and people and will always be a club that remains close to my heart.
"I have thoroughly enjoyed my time there, made some lifelong friends. I can't thank them enough for giving me the opportunity and for their continued support.
"At this moment in time though I feel the decision to move to France is the best career opportunity for me personally as a professional rugby player.
"As well as the rugby challenges, I'm looking forward to experiencing and embracing a new culture and learning a new language. However, until then I'm completely focused on performing for the Blues and Wales."