Ashton, who enjoyed a sensational season last term, will leave Northampton in the summer after agreeing what is believed to be a three-year contract with the reigning Aviva Premiership Champions.
"Chris Ashton has signed a long-term contract with Saracens, and the England wing will join the north London club at the start of the 2012/13 season," said a Sarries statement.
"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."
Former rugby league sensation Ashton joined Northampton from Wigan Warriors in 2007 and has scored a remarkable 90 tries in 105 games for the club.
His scoring record is just as impressive in the Test arena where he boasts a tally of 15 tries in 18 internationals for England.
He finished the 2011 RBS 6 Nations as top try scorer with a joint championship record six scores, while his four tries in the win over Italy is a record for a single match in the tournament.
Ashton is unsurprisingly one of the favourites for a Test berth on the 2013 Lions tour of Australia but the nature of his long drawn out transfer saga is likely to have repercussions on the remainder of his time with Northampton.
Saints boss Jim Mallinder and Ashton were reportedly involved in a training ground row earlier this week and Ashton is now expected to be overlooked for this weekend's Heineken Cup clash with Munster at Franklin's Gardens.