The Samoan-born England international, who is out of action with a long-term groin injury, agreed to a deal that will earn the 24-year-old more than £425,000-a-year with the East Midlands club.
The contract puts him among the world's richest players, and Tigers director of rugby Richard Cockerill praised Tuilagi's loyalty after he knocked back lucrative offers from Wasps, Worcester, Saracens and Toulouse.
"Manu is in the prime of his rugby life," Cockerill told the Daily Mail.