Davies, 25, from Carmarthenshire who joined the Scarlets as a teenage academy player is one of a number of talented young West Wales players enjoying international success after coming through the Scarlets rugby development pathway.
Now into his eighth season with the Scarlets, Davies was named co-captain this season alongside Scarlets number eight Rob McCusker and has appeared 111 times for the Scarlets with 185 and 37 tries points to his name. He has 37 caps for Wales and three for the British and Irish Lions.
It will be Davies' first move of his rugby club career following his outstanding contribution to the Lions tour to Australia this summer, which firmly established him as one of the very best centres in World rugby.
Davies was born in Solihull, Birmingham before moving with his family at a young age to Bancyfelin, St Clears. He attended Dyffryn Tâf Comprehensive School before going on to study Sports and Exercise at Trinity College, Carmarthen.
Mark Davies, Chief Executive of the Scarlets said: "For everyone in the region retaining Jon within the Scarlets squad has been one of our highest priorities since the middle of last season.
"Jon's contribution to both our squad, clubs and our schools around the region has always been a real example of the philosophy of the club in encouraging ambition and the development of talent that exists across three counties.
"Whilst we have done everything in our power as a club and as a business to ensure Jon could continue to play his rugby with Scarlets, his outstanding performances on the World stage have of course meant that he has been targeted by several other major clubs with very significant resources for some considerable time.
"Jon has taken as much time as he could to consider each element of the tremendous opportunities available to him and has ultimately now had to make his decision on the best route for him as an individual at this point in his rugby career.
"Unfortunately for us that will result in Jon playing in France over the period of his next contract but we remain immensely proud of everything Jon has achieved with his region and completely respect his decision to extend his horizons and take this significant opportunity at this time.
"When we reach the end of the season, he will leave as a true Scarlet with all our thanks for everything he has given to the Scarlets shirt and our very best wishes for success at another great club."
Scarlets Head Coach Simon Easterby said: "Jon has established himself in recent seasons as a world-class centre for Scarlets, Wales and now the British and Irish Lions. He has worked hard throughout his career to date and has now shown his ability on the highest of rugby stages having grown into his role as a senior player here in our region.
"He has gained valuable experience and developed quickly with the Scarlets in recent years as part of a group of young internationals that are from our region and have successfully gone onto achieve honours with Wales.
"He has always taken great pride in having his rugby roots in West Wales and I know this will have been a tough decision for him personally, and probably one of head over heart. His commitment to our region during this, the first part of his rugby career has been evident and I know that having grown up in our region he will always want to be closely associated with Scarlets rugby now and in the future.
"He will give his all in his last season with us I am sure and will lead from the front. But for now, our focus is to support Jon as he recovers from his injury and gets back to full fitness as soon as possible."