He joined the Saints from near-neighbours Bedford Blues in 2006 and made his debut in the opening game of that season's Guinness Premiership. Tonga'uiha has scored 10 tries in his 99 appearances to date, including two this season.
"Soane has really knuckled down in the past couple of seasons and is starting to play to his potential," said Saints director of rugby Jim Mallinder.
"He is still relatively young for a prop and has plenty of years left in him. But he will have to play extremely well tomorrow, as will the rest of the team, against a talented London Irish outfit.
"They like to play a constructive style of rugby and score a lot of tries. They also have good kickers too, like Ryan Lamb, Chris Malone and Peter Hewat, and are able to keep the score board ticking over.
"If we are to get a positive result we will have to play with control, impose our game plan and be as clinical as we were in the second half against Worcester."
Saturday's game is sold out, but Saints supporters can follow the action from Franklin's Gardens in a number of ways.
There will be text tracking on Matchday Live and score updates will be published every 10 minutes on the club's Twitter feed, www.twitter.com/SaintsRugby, which is also available on your mobile phone - great if you're out and about in the shopping sales!
NORTHAMPTON SAINTS TEAM TO PLAY LONDON IRISH
Guinness Premiership Round 12
Franklin's Gardens
Saturday, January 2nd, 2010
Kick off 3:00pm
15 Ben Foden
14 Chris Ashton
13 Jon Clarke
12 James Downey
11 Paul Diggin
10 Stephen Myler
9 Lee Dickson
1 Soane Tonga'uiha
2 Dylan Hartley (capt)
3 Euan Murray
4 Ignacio Fernandez Lobbe
5 Juandre Kruger
6 Courtney Lawes
7 Phil Dowson
8 Roger Wilson
Replacements
16 Brett Sharman
17 Jon Vickers
18 Brian Mujati
19 Christian Day
20 Neil Best
21 Alan Dickens
22 Shane Geraghty
23 Chris Mayor
