The fan favourite, who has formed a solid defensive partnership with Luke Chambers this season, was due to be out-of-contract at the end of the 2013/14 campaign has signed a continuation of his contract to remain as a Blue.
“I’m delighted to extend my stay at Town,” Smith said. “It’s great that the club have shown loyalty with me and that I’ve shown my loyalty to the club as well.
“I’ve been here since I was 16 years old and I love the club. Hopefully I can be here for a few more years to come and we can be successful. The club means a lot to me and I’ve developed a great relationship with the fans.”
Smith featured in the 2010 World Cup and last year’s OFC Nations Cup and London Olympics for New Zealand has made 112 appearances for the Blues, scoring 10 goals.
The 23-year-old has also had loan spells at Brentford, Colchester and Stevenage.