The 24-year-old, who made his international debut this year in the three-match Test series with Wales, is part of the All Blacks squad for Sunday's Rugby Championship match against Argentina.
Tamanivalu is now looking ahead to a new challenge after two years with Chiefs.
"I am grateful for my time at the Chiefs and everything I have learned there, but this is a fantastic opportunity for me to develop in a different environment," he told the club's official website.
"I have long respected the Crusaders as a highly driven and successful team, so I am excited to be a part of that next year."
Coach Scott Robertson added: "Seta is such an impressive player and will add some real power and strength to our backline in 2017.
"He is exactly the sort of player we have been looking for to complement our squad, so we couldn't be more excited to have him on board."
Crusaders were beaten quarter-finalists in the 2016 Super Rugby campaign.