Jack told a media conference in Christchurch that it had been a difficult decision to quit New Zealand rugby but he had decided to put his wife and family first.
Jack has been with the Crusaders since 1999 playing 87 matches for the defending Super rugby champions.
According to the New Zealand Press Association (NZPA), Crusaders’ coach Robbie Deans said Jack’s departure would be a huge loss for the Crusaders and New Zealand rugby but no-one would begrudge him and wife Kym an opportunity to see the world.
During his time with the Crusaders Jack shared in five Super rugby titles and two other finals.
He made the All Blacks in 2001, was player of the year in 2002 and is the fourth most capped lock in All Blacks’ history with 57 caps.
Jack damaged his hamstring against the Waratahs in Sydney last month but is expected to return to the Crusaders lineup before the end of the Super 14 season.
Jack’s departure follows news that All Blacks prop Carl Hayman will play for English club Newcastle next year.
Scrum-half Byron Kelleher earlier announced he would join French side Agen for two years at the end of the year.
Aaron Mauger and Sam Tuitupou will also play overseas after the Cup, while All Blacks hooker Anton Oliver is also poised to move offshore after this year.