Wales fly-half Dan Biggar feels "hugely privileged" to be joining Aviva Premiership club Northampton.
Saints have announced that Biggar, 27, will move to Franklin's Gardens from the Ospreys next summer.
He is currently on a national dual contract funded by the Ospreys and the Welsh Rugby Union.
In a joint statement, Biggar's regional team and the WRU said he declined an option to extend the deal "under significantly improved terms".
When Biggar moves to the East Midlands, his immediate Wales prospects will hinge on him securing one of four wildcards available to head coach Warren Gatland next season - under the WRU's senior selection policy for players based with clubs outside Wales.
That figure drops to just two wildcards in 2019-20, which is also a World Cup season.
Biggar, who has won 56 caps and toured New Zealand with the British and Irish Lions earlier this summer, will follow his Wales international colleague George North to Northampton.
"I am hugely privileged to sign for a club with the history and tradition of Saints," Biggar said.
"It is extremely exciting to start a new chapter of my career with a club that shares my ambition to win trophies, which is where this club belongs.
"I have to say a massive thank you to the coaches and board for the confidence put in me, and I look forward to working as hard as I ever have in my career to return the faith.
"This is an opportunity for me and my family to experience rugby in a different environment, and playing in a town and surrounding area which has a massive passion for rugby was a huge attraction.
"I would like to thank everyone at the Ospreys and the Welsh Rugby Union who has supported and helped me throughout my career, and an extra special thank you to the fans who have helped and supported me through highs and lows.
"To play for my home club was a dream come true, let alone to play as many times as I have done.
"I hope my passion for the shirt and people of this region has shone through in my performances, and I would love to leave on a high note with some silverware. I also remain fully committed to Wales and achieving the best I can every time I pull on the red shirt."
Northampton rugby director Jim Mallinder hailed Biggar's signing, adding: "We are delighted to have secured the signature of such a highly-rated player.
"Dan has shown his excellence year in, year out, for both the Ospreys and Wales, and he performed really well for the Lions this summer.
"The fact that he has put pen to paper a year in advance shows that Dan has plenty of belief in where we are going as a club and our ambitions for the future, and we are looking forward to welcoming him here next summer."
Biggar, who made his Test debut in 2008, has scored 295 points for his country, putting him sixth on Wales' all-time list.