Papali'i enjoyed a breakout campaign in his first season with the Eels this year, being named Dally M Second Rower of the Year following his efforts in the blue and gold.
The 23-year-old played 25 games for Parramatta in 2021, proving to be a try-scoring threat in attack while also boasting a strong tackling rate and running game.
After reaching new heights with the Eels following his departure from the Warriors at the conclusion of last year, the Samoan and New Zealand internaitonal's stocks quickly soared, placing some concern on Parramatta's books for the future.
Papali'i has gained interest from the Dolphins, with the NRL's newcomers having their advances knocked back by the Parramatta star.
However, the Tigers have swooped on Papali'i's asking price of more than $600,000-per-season, a fee the Eels reportedly struggled to compete with.
"The Club worked with Isaiah and his management team to remain with the Club beyond his current contract including a significant upgrade for 2022, however he has chosen to take up an offer with another Club," Parramatta wrote in a club statement.
"Isaiah made a terrific contribution and has provided great value to the Club in 2021, and both Isaiah and the Club are committed to another strong year in the Blue and Gold in 2022."
The departure of Papali'i follows Marata Niukore's exit to the Warriors for 2023, with the Eels forward also understood to earn a significant wage with his new club.
“Isaiah is an exceptionally talented young forward who has shown himself to be a player with a fantastic attitude, work-ethic and drive,” Sheens said in a statement.
“We firmly believe that his best football is still ahead of him and we’re very excited to see him progress in next steps of his rugby league career with Wests Tigers.”
Both players will remain in Parramatta for next season before departing for their new clubs.
The twin departures are set to open some wiggle room for the Eels' financial planning for 2023 and beyond, with the likes of Clint Gutherson, Reed Mahoney, Dylan Brown, Haze Dunster, Ryan Matterson, Maika Sivo and Junior Paulo among those not signed past next year.