Following reports he had inked a $13 million, 10-year deal to join the Knights from 2026, Brown took to social media to confirm he would leave the Eels at season's end.
That deal is not yet official, but if finalised would eclipse a 10-year, $12 million contract signed by Gold Coast forward Tino Fa'asuamaleaui in 2023.
Brown's exit shapes as a devastating blow to the rebuilding Eels, who suffered a heavy 56-18 loss to Melbourne in the first game of Jason Ryles's coaching tenure on Sunday.
"Hello everyone, I have decided to take an opportunity that is best for me and my family," Brown wrote on Instagram.
"To the Blue and Gold family ... nothing changes. I'm locked in for this year and we have a job to do. Love."
The Knights and an unidentified Sydney club were jostling for Brown's services but AAP has been told Newcastle are confident of a deal being done.
Once an offer is accepted by Brown and manager Chris Orr, NRL rules stipulate a 10-day cooling-off period, which the Eels could use to try to convince the 24-year-old to stay put.
But barring a change of heart, Brown will join forces with star fullback Kalyn Ponga in a supercharged Knights spine from 2026.
Parramatta confirmed on Monday night that Brown would leave the club at the end of the season, saying he had agreed to terms with another club.
"Dylan has been offered what I understand to be the biggest deal in NRL history from 2026 onwards," the Eels' general manager of football  Mark O'Neill said in a statement.
"Dylan is a class player, we understand his decision to take up the offer and no one could begrudge him for accepting this opportunity for him and his family."Despite agreeing to terms with another NRL club for future seasons, Dylan remains committed to the Eels in 2025 and we look forward to him playing his role in the team for the remainder of the year."
Newcastle have long struggled for consistency in their halves, notably failing to settle on a combination even on the run to finals in 2024.
In New Zealand international Brown they would have a talented ball-runner who could provide extra playmaking spark next to Ponga, the club's primary creative outlet in recent years.
The Eels will now be forced back to the drawing board only weeks into the Ryles era.
Less than two weeks ago, the club flagged plans to continue building around their existing halves pairing by re-signing halfback Mitch Moses to a long-term deal.
Moses himself had voiced his hopes that Brown would choose to remain at Parramatta.
The five-eighth had re-signed in 2022 on a contract with clauses allowing him to stay until 2031 if he wanted.
But 2025 was the last guaranteed year of that deal and Brown had been able to negotiate with rival clubs since last November.
The Eels are now set to turn their attention to their own future, but there is a shortage of elite halves coming off contract at the end of this season.
Sean O'Sullivan, Brad Schneider, Adam Doueihi and Will Pryce are solid playmakers available, but none of those men are first-choice halves at their current clubs.
Other options including Daly Cherry-Evans, Adam Reynolds and Chad Townsend, are deep into their 30s and are not guaranteed to play on into 2026.
