North will arrive at Franklin's Gardens this summer on a three-year contract after his release from the Scarlets was secured with 12 months of an existing deal still remaining. He follows fellow new arrivals in England prop Alex Corbisiero and Samoa scrum-half Kahn Fotuali'i, who have been recruited from London Irish and the Ospreys respectively.
"We have worked very hard over recent years to put Saints into a strong and sustainable financial position where we can build a squad that includes world-class players and has credible prospects for silverware," Robson said.
"We are determined to bring success to Franklin's Gardens, and signing players like George, Kahn Fotuali'i and Alex Corbisiero - all of whom are regarded as being among the best in their positions anywhere in the game - is a very important part of that.
"Over recent weeks there have been plenty of negotiations between ourselves, the Scarlets management and George's representatives, and we believe that we have come to an agreement which is in the best interests of both clubs and the player himself."
North has won 31 caps and although no figures have been released, it is likely that Saints will pay the Scarlets around £200,000 to seal North's early contractual release. North, himself, could command an annual salary of around £250,000 at Franklin's Gardens after becoming the latest high-profile Wales international player to quit the Principality.
The likes of his RBS 6 Nations title-winning colleagues Mike Phillips, James Hook and Gethin Jenkins all currently play in France, while centre Jamie Roberts and flanker Dan Lydiate are expected to join wealthy Parisians Racing Metro this summer.
Scarlets chief executive Mark Davies said: "Despite our desire to retain all our internationals within the region, we have to balance our available resource over the need to sustain a 50-deep player squad that can continue to compete during international periods. Taking that into account, we made George the very best offer we could.
"However, we have to fully understand and appreciate that George's quite unique value in the rugby marketplace, possibly inside Wales, but certainly outside Wales, is considerably greater than the Scarlets as an independent business can reach."
Davies said the Scarlets contacted 20-year-old North's representatives more than two months ago immediately following a direct approach for his services from a club outside the United Kingdom.