"This has been an incredibly hard decision," North, who has 69 caps for Wales, said in a club statement.
"Saints have developed me as a player and stuck by me through thick and thin, so it is with a heavy heart that I have decided to move on.
"I love playing for Northampton Saints and am excited by the potential of the squad that is being assembled but, as a proud Welshman, I felt that now is the right time to move back home despite the compelling offer Saints made me."
North made six appearances for the club this season before being sidelined last month by a knee injury that will require six to eight weeks' rehabilitation.
Wales coach Warren Gatland said a decision on which team North will join will be made in the coming months.
"It is fantastic that George is returning to Wales on a National Dual Contract," Gatland told WRU's website. (www.wru.co.uk).
"We will work with George to determine the best fit for him and will look to announce where he will play in the New Year."
(Reporting by Hardik Vyas in Bengaluru; editing by John Stonestreet)
