Witts was set to become an unrestricted free agent at the end of the season and other clubs were circling the 33-year-old after he lost his No.1 ruck mantle to 24-year-old Ned Moyle.
But Witts wants to end his career at the Suns, with his new deal to take him to his 36th birthday if Gold Coast make a deep finals run in 2028.
With Moyle now the clear top ruckman at the Suns, there's no guarantee of game time for Witts in the next two years.
Moyle tallied an incredible 60 hitouts in last week's two-point win over GWS and will again lead the ruck in Saturday's clash with the Brisbane Lions at the Gabba.
Hardwick was full of praise for the manner in which Witts has handled losing the No.1 ruck role.
"He's very selfless. It's one of the reasons he was the captain of this footy club for a long time," Hardwick said.
"Jarrod's not about himself; he just wants to see this club succeed and he'll give everything to do that.
"That's why he's been nothing but incredibly supportive of Ned.
"Obviously we're playing Ned more so than Jarrod, but he's pushing him up in everything he can do. He helps him through training, goes through his vision to educate.
"So that's the the mark of a man. He's such an important piece of the fabric of this club."
Hardwick described Witts as one of the "pinnacles' of the Suns.
"He's sought after from other clubs, but his heart is certainly at this football club and we're pumped that he's decided to stay on," Hardwick added.
"He feels this football club is part of his legacy, and he wants to make sure that he continues the journey and sees it out to where he thinks this football club can go."
Gold Coast (8-13) are already out of the race for a wildcard finals berth, while two-time defending premiers Brisbane (14-7) need a win to bolster their top-four hopes.
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