The 25-year-old has agreed a deal that will keep him at Sixways until 2010.
He will link up with the Warriors in November after the World Cup and New Zealand's national provincial competition have been completed.
Tuitupou has won nine caps for the All Blacks, and is a former New Zealand under-19 and under-21 captain. He is also an Auckland Blues regular in the Super 14 competition.
Worcester rugby director John Brain said: "This is clearly an important signing for Worcester.
"In Sam, we have not just signed an explosive 'go forward' player, but one who at a comparatively young age can offer us a wealth of experience playing at the very top level. It is very exciting news for the club."
What level of rugby Tuitupou will play at though, is unclear, as Worcester are currently involved in a fight for Premiership survival, standing one point above bottom club Northampton with just three games left.