Soliola, 25, joined the club from Sydney Roosters ahead of the 2010 season and has since made 43 appearances for Saints.
He said: “There was never any doubt that I would sign for the Saints. I have enjoyed my time at the club and I am looking forward to a successful season in our brand new stadium.
“We have a lot of strength in depth at Saints and I’m sure we will be challenging on all fronts this year.”
Despite ankle and knee problems during his time at the club, Soliola helped the club to reach the Grand Final in 2011, where they beaten by Leeds.
Chairman Eamonn McManus said: “We are delighted to lock down Sia to a long-term deal. He has been one of our standout performers this season and at 25 years of age is still improving.
“He is a proven International and alongside some of the fantastic products from our famed Academy will form the hub of the side for many years to come.”
Soliola has played in eight of Saints’ 10 Super League games this term, scoring four tries.