The champion forward's confidence in his problematic knee was illustrated by the fact he played every game last season, winning a record sixth best and fairest award, booting 49 goals and leading the AFL in marks.
Coach Alan Richardson said Riewoldt's influence on and off the field was exceptional for such a young group.
"Nick's re-signing is fantastic for our football club,” Richardson told the Saints' website.
"He sets a tremendous example to our young players on how to prepare for AFL football. His commitment to leave a strong legacy, that he’s carried on from the likes of Robert Harvey and Nathan Burke in the early 2000s, is a credit to him.
"His personal legacy is intact, but he has this deep desire to leave one for the football club and that is why he is so widely respected both externally and internally."
That Riewoldt, the No. 1 pick in the 2000 NAB AFL Draft, was named an All Australian for the fifth time in his career in 2014 is testament to his standing in the game.
After watching Riewoldt represent Australia in Saturday's International Rules Series against Ireland, Richardson said he saw no reason why the captain couldn't keep playing beyond 2016.
"Barring any major mishap or injury, Nick could definitely play beyond the contract he’s just signed, but that’s a fair way down the track," Richardson said.
"For the moment we’re just delighted to have Rooey with us for another two seasons and leading the regeneration of our playing group."
Premiership Pie on GF glory, overcoming adversity, his best role
Billy Frampton's trade to Collingwood went all but unnoticed at the time, but he has now become an important part of the puzzle
X marks the spot: Giant making an impact in new role
Xavier O'Halloran is making his mark in the Giants' midfield
From raw prospect to No.1 ruck, Power recruit takes the long road
After nearly a decade as a back-up ruck option at Richmond, Ivan Soldo made the switch to Port Adelaide and is recording career-high numbers across the board
Analysis
Analysis
Middle men: Inside the organised chaos of a centre bounce battle
Cal Twomey dives into the planning, tactics, match-ups, data and strategy that go into a centre bounce encounter