Crusaders snare All Black centre Tamanivalu
Coach Scott Robertson said it was "incredibly exciting" to bring Tamanivalu to the seven-time champions. He previously played for the Chiefs.
"Seta is such an impressive player, and will add some real power and strength to our backline in 2017," Robertson said.
"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."
Fiji-born Tamanivalu, 24, has three Test caps after making his All Blacks debut against Wales in June.
He will join former Wallaby Digby Ioane at the Crusaders as the Christchurch-based team seek to end a title drought stretching back to 2008.
The Chiefs are believed to have attempted to retain Tamanivalu but have rising talent Anton Liernert-Brown ready to take his palce.