The fullback was officially unveiled to the French media this week and will link up with the Top 14 champions following the World Cup.
Byrne had been contracted to another season at the Ospreys but they allowed his early released and he has signed a three-year-deal with Clermont.
Hefollows in the footsteps of fellow Welsh Lions James Hook, who is joining Perpignan, and Gavin Henson, who has signed for Toulon via Saracens, out of the Liberty Stadium.
And Byrne, who made four appearances for the Lions is South Africa before getting injured, reckons he has joined the best league in the world.
"This is the best choice for me," said Byrne.
"I'm aware of the history and great ambition here at Clermont.
"I have been impressed by the club, the stadium and the facilities. The club want to win trophies and so do I.
"I played here last year for the Ospreys in the Heineken Cup and the atmosphere was incredible.
"The French Championship is probably the best league in the world. More and more world class players want to come here and I hope to produce some of the best rugby of my career here when I eventually start playing.
"I had a tour of the city and I've found the place to be charming."