Fifita told Roosters officials on Thursday he would take up a four-year deal with the NRL club, worth close to $3.3 million over four years.
The signing coup will help the Tricolours replace some of the X-factor they lose with the impending departures of Joey Manu and Joseph Aukuso-Suaalii this year.
Veterans Luke Keary and Jared Waerea-Hargreaves will also finish up in the NRL this year, leaving the Roosters without 1000 games of experience.
"You want quality players, and (Fifita) is a quality player," Roosters lock Victor Radley told AAP on Thursday.
"He's got the footwork, he's a powerhouse. Fast. You don't have many players that do all those things.
"He's got the X-factor."
David Fifita crashes over in the Titans' round-seven loss to Manly. (Jason O'BRIEN/AAP PHOTOS)
The news comes as a blow to both the Titans and Panthers.
The superstar second-rower had met with Gold Coast officials on Wednesday night, before officially confirming he would not activate the final two years of his contract there.
Coach Des Hasler insisted on Thursday he did not feel personally slighted by Fifita's decision, and denied he was abandoning ship.
Re-signed to the Titans last year when Justin Holbrook was in charge, Fifita's decision to exit the club comes after a 1-7 start to begin this year.
"I think that is unfair to say that he is abandoning the ship," Hasler said.
"He has made a decision. It is not about abandoning ships. Everybody knew what was on the table.
"Not at all (do I take it personally). It is a decision Dave has made. We move on and keep playing.
"It is disappointing, but it is all a part of the game and part of the theatre. It is part of the football merry-go-round that footballers come and go all the time."
Fifita's exit will free up the Titans' salary cap from next year, and offers a chance to spend big on their next playmaker once Kieran Foran retires.
Hasler said he was not concerned about Tino Fa'asuamaleaui pulling a similar option in the future, given he is signed until 2033 but with options in his favour from 2027.
Titans teammates Tino Fa'asuamaleaui and David Fifita at training. (Dave Hunt/AAP PHOTOS)
Penrith had initially been considered the front runner for the 24-year-old's services, before being informed on Thursday they had missed out.
Keen to fill the void set to be left by James Fisher-Harris' looming departure, the Panthers had planned on shifting Scott Sorenson into the front row next year to accommodate Fifita.
As three-time defending champions, the Panthers were also theoretically in the best position to convince Fifita they could make him a premiership winner.
But the wrecking-ball edge forward has instead opted to try and win that title at the Roosters.
His signing could also have implications in the NRLW, with Fifita's partner Shaylee Bent off contract at the end of 2024 at the Titans and also able to join the Roosters.
Penrith could now turn their eye to off-contract Rooster Angus Crichton as their solution in the pack.
The Panthers made an inquiry late last week with the 28-year-old's management to get a lay of the land on his future options.
Crichton has previously expressed a desire to make a code switch to rugby union, and is exploring the option of linking with a French club.
He could also theoretically fit into the Roosters' cap, but that would leave either he, Fifita or Sitili Tupouniua playing off the bench.
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