Fijian-born Tamanivalu, 24, will shift from the Chiefs, for whom he played 22 games over the last two seasons.
His form was good enough to earn an international call-up, making three bench appearances. Two came against Wales in June and another against Australia in Wellington a month ago.
Incoming Crusaders coach Scott Robertson says Tamanivalu will add power to a backline which is without departed powerhouse winger Nemani Nadolo.
“Seta is such an impressive player, and will add some real power and strength to our backline. He is exactly the sort of player we have been looking for,” Robertson said.
A former Fiji under-18 rugby league representative, Tamanivalu shifted to Auckland in his late teens.
He stood out for Taranaki at domestic level, being named NPC player of the year in 2014.