Assuming he sees out the deal which runs until the end of 2027, O'Brien will overtake Michael Hagan as the Knights' most-capped mentor.
The extension seals a remarkable turnaround for O'Brien, who was under pressure to retain his job when the Knights were struggling outside of the top eight midway through last season after finishing 14th in 2022.
But off the back of a Kalyn Ponga tidal wave and several unsung stars stepping up, the Knights were able to claim their first home final since 2006.
Their form to finish last year has ensured O'Brien's long-term future, but the coach wants his legacy to be measured by one metric.
"There's a couple of guys that have got some silverware there that I'd like to have," O'Brien said on Thursday.
"But I'm really proud to be one of the leaders of this club and I'm right where I want to be.
"Milestones are great but that's further down the track for me to reminisce on."
Only Mal Reilly (1997) and Hagan (2001) have won premierships with the Knights.
O'Brien's extension comes just days after the Knights fended off interest from rivals to lock in strike centre Bradman Best until the end of 2027.
With Best, Ponga, the Saifiti twins and now O'Brien all signed up for the long term, the Knights coach is hoping they can build on their dazzling end to 2023.
"We're closer than we have been for a long time," O'Brien said.
"How close? It's a hard one to answer but we approach every single day with a winning mindset that we come in here and make sure that we're handling the process that will take care of that silverware.
"That's a result of hard work and we've done a really good job at the back end of last year and over the summer.
"Ultimately we need to go out and perform now so if that gets us there this year, I would be rapt.
"I'm not sure when it will but I know that we're heading in the right direction."
O'Brien's deal means master mentors Wayne Bennett and Craig Bellamy are the only active coaches off contract for 2024.
Bennett has confirmed he will leave the Dolphins at the end of this season, while Bellamy's future has long been a year-by-year prospect at Melbourne.
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