The versatile prop, who can play both sides of the scrum, will join London Irish after the World Cup in October.
“I am really looking forward to joining London Irish,” he said in a statement.
"I have been to have a look around Hazelwood and was very impressed with the setup. After speaking to the board and seeing the facilities, the ambition of the club is clear.
"It is a family-friendly club which played a big part in my decision to move my family over. London Irish also has a link with St Mary's University, where I will be able to study alongside playing rugby for the club.
"There is still work to be done in New Zealand, but my family and I are looking forward to joining the club next season."
After starting out his career at the Crusaders, Franks moved to the capital in 2013 and has made 42 caps for the All Blacks.
He joins the likes of Dan Carter, Jeremy Thrush and Ma’a Nonu who have also signed lucrative contracts overseas.