Off contract at the end of next year, Garner had been given permission by the Panthers to see if he could find a longer deal elsewhere.
But the 29-year-old will now remain at Penrith by mutual agreement, after having his most consistent season since arriving in 2023.
"My understanding is he is staying, which is great," coach Ivan Cleary said.
"We always wanted him to stay. It was one of the situations where if he can have a look and extend you maybe think about it.
"But we're really happy, he is playing great footy and looking forward to the future with him.
"He has been really good for us which we've needed."
Penrith have decisions to make in their back row ahead of the finals, as they edge towards full fitness.
Liam Martin is some chance of making his return against Wests Tigers on Saturday, after suffering a fractured hand in State of Origin III.
Scott Sorensen will miss the CommBank Stadium clash with injury, but is expected to return in coming weeks.
Half Nathan Cleary is meanwhile close to resuming goalkicking following his groin issue, while Brian To'o has also been cleared of any fresh injury after a knee knock last week.
Penrith's return to fitness could not have come at a more threatening time for the rest of the NRL, following six straight wins after sitting last in June.
They have conceded just 11 points a game through those six victories, taking their defence back to the same levels as through their four premiership years.
Crucially, that has also come through a time where their five State of Origin stars have been in and out of camp, rarely able to train with the team.
Penrith have won grand finals in almost every way during their four-year romp, with nail-biters, comebacks and utter dominations.
But the Panthers' poor start has presented Penrith with a different kind of challenge to defend this year's title, and still loom as a genuine chance come finals.
"I wouldn't have scripted it that way if I didn't have to," Cleary said.
"It's definitely a different season for us and a challenge that is new. I have certainly coached teams that have been down the bottom before.
"From where we have come from it is definitely unchartered waters.
"I'm just really happy with the middle part of the year. The Origin period's always hard for us, but this year in particular after the way we started.
"I'm really happy with the way we navigated through that, and our best footy is in front of us which is exciting."
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