The deal will be two years in length, meaning Fitzgibbon will remain with the Knights until at least the end of the 2023 season.
Fitzgibbon may not have made his way into a the first grade set up on a full time basis until he was 24 years of age during the 2018 season, but the now 27-year-old has become a critically important cog in Adam O'Brien's side.
While he missed most of the first half of the season, Fitzgibbon started every game between Round 9 and 16, and while he has missed a few since the competition moved to Queensland as O'Brien attempts to work out his best 17, to go with injury concerns, the now 89-gamer is an important retention for the Knights.
In his ten games this season, he has scored three tries - a solid result for a forward in the second-worst attack in the competition. He has also added four line breaks, six offloads and tackles at almost 96 per cent while averaging just under 100 metres per game.
Tyson Frizell's arrival at the club, to go with the continued good form of Mitch Barnett and Brodie Jones as given O'Brien a selection headache, but Fitzgibbon had no intentions of going anywhere else.
“I’ve been with the Club now since 2013, I’m a Novocastrian boy and I couldn’t see myself playing in any other colours,” Fitzgibbon said.
“We’re starting to see the improvement of our squad over the last two years with Adam and we’re looking at some bigger and better things in the near future."
Fitzgibbon failed to be selected for this weekend's clash with the Brisbane Broncos, it serving as a dead rubber ahead of the finals, which the Knights will enter from seventh spot on the competition table.