Saracens have completed the signing of Northampton and England wing Chris Ashton on a "long-term" contract.
The 24-year-old, whose Saints deal expires in the summer, will join Sarries for the 2012-13 campaign.
The length of Ashton's deal has not been disclosed by the reigning Premiership champions.
"I've decided to join Saracens from next season... until then it's all about Saints," he said on social networking site Twitter.
A spokesman for Saracens added: "We are obviously especially delighted but, for now, Chris remains a Northampton player.
"Out of respect for Saints, Saracens will not make any further comment on the matter."
BBC Look East understands that Saints director of rugby Jim Mallinder will not include Ashton in his starting line-up for Saturday's Heineken Cup Pool One visit of Munster.
The move brings to an end months of speculation over the future of Ashton, who has been allowed to speak to other clubs since New Year's Day.
Saints had said they would not break the bank to keep him at the club, but it is understood that the player's eagerness to leave was motivated more by a desire for a change of scenery after four years at Franklin's Gardens.
Reacting to Ashton's departure, Mallinder said: "We're obviously disappointed that Chris has decided he wants to play his rugby elsewhere.
"That said, we have known for some time that Chris was looking elsewhere and had been planning to use that part of the salary cap by strengthening our squad in a number of positions.
"We've also got several good wingers at the club who have all been pushing for a first team spot this season, the likes of Jamie Elliott, Vasily Artemyev, Scott Armstrong, Paul Diggin and Noah Cato, plus Anders Mogensen in the academy who has been playing well on loan for Cambridge."
Ashton has made 105 appearances for Northampton, scoring 95 tries, since his cross-code switch from Wigan in 2007.
He will now join up with his friend Joel Tomkins, the former Wigan and Great Britain rugby league player.
But he will leave Northampton with a big gap to fill having proved he is a devastating finisher.
Although he has drawn negative publicity recently, having been banned for four weeks for pulling the hair of Leicester's Alesana Tuilagi and being reprimanded while at the Rugby World Cup, he was also the tournament's joint-top try scorer and has totalled 15 tries in 18 Tests for England.