The new deal will see the Tongan through to 2016 at the Madejski Stadium.
Halavatau, who joined the club after one year at Birmingham & Solihull, believes that it is an "exciting time" to be playing for the Exiles.
"I have really enjoyed the year and a half I have spent at the club and I'm thrilled to be staying on for a further three seasons," said the 28-year-old.
"There are some incredibly talented players in the squad and we believe we can compete with the best teams in the league so it is an exciting time to be involved with London Irish."
Halavatau has seen his playing time limited to just four appearances this season due to a calf injury.