It comes as Brisbane signed North Queensland's back-up halfback Tom Duffy for 2026.
Prop Iszac has signed a two-year deal with the France-based club, which has also recently lured unwanted Bulldog Toby Sexton and Wests Tigers centre Solomona Faataape.
Captain Tino started his NRL career in Melbourne, but Iszac came through the Titans development pathways and has played 25 matches over three seasons, including 11 off the bench this season.
The 23-year-old told the Catalans club website he was looking forward to improving his game under their new coach, former England international Joel Tomkins.
"It's a great opportunity for me to improve my game, gain experience, and be a part of what Joel Tomkins is building within the playing group," Iszac said.
"I'm also looking forward to living in such a beautiful part of the world in the south of France and experiencing it all with my family."
The elder Fa'asuamaleaui, who has notched 108 NRL games, 15 State of Origin caps with Queensland and has played six matches for the Kangaroos, is set to test the open market.
He has a 10-year deal at the last-placed Titans until 2033 but has get-out clauses, the first at the end of next season.
The superstar lock is believed to be in the sights of NRL newcomers the Perth Bears, Canterbury and St George Illawarra.
The 25-year-old has also been linked back to competition heavyweights Melbourne after tasting premiership success with the Storm in 2020.
Duffy will join the Broncos next season after falling down the pecking order in his rookie season at the underachieving Cowboys.
The Cowboys' decision to re-sign fellow playmaker Jake Clifford spelt bad news for Duffy last month, with the 22-year-old Townsville product inking a one-year deal at the Broncos.
Duffy has played six NRL games to date and is set to join Ben Hunt in providing depth behind first-choice playmakers Adam Reynolds and Ezra Mam.
"I think there's probably not a better club to go to at the moment as a half if you want to develop your game," Duffy said.
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