New England is giving Brown a one-year deal worth up to $15 million, Rosenhaus said. It includes a $9 million signing bonus, $10 million guaranteed and $5 million in incentives.
The agreement came hours after Oakland released Brown to end his tumultuous stint with the Raiders, who acquired the Pro Bowl wide receiver via trade during the offseason.
Brown took to social media after he agreed to the deal.
Brown was eligible to sign with any team at 4:01 p.m. ET Saturday. He is not eligible to play until Week 2 at the earliest, which means he will miss New England's opener Sunday night against his former team, the Pittsburgh Steelers. The Patriots and Raiders do not play this regular season.
The Patriots will have to make a corresponding move once they officially sign Brown, but for now, their receiving corps includes Super Bowl LIII Most Valuable Player Julian Edelman, Brown, Josh Gordon, Demaryius Thomas, Phillip Dorsett and undrafted rookies Jakobi Meyers and Gunner Olszewski. First-round draft choice N'Keal Harry has opened the season on injured reserve.
Brown asked to be released by the Raiders in an Instagram post earlier Saturday. Oakland had fined him $215,073.53 for conduct detrimental to the team, sources told Schefter, a move that voided the $29.125 million of guaranteed money in Brown's deal.
In addition, the Raiders sent Brown a letter stating that he no longer would be entitled to termination pay, sources told Schefter. As a result, Brown would have been playing on a week-to-week basis with both his guaranteed money voided and lack of termination pay.
Oakland, in turn, cut Brown just before noon Saturday.
"Technically, it was really more of a warning," Rosenhaus said on SportsCenter, referring to the removal of the guarantees. "If there were any infractions down the line, the Raiders would protect themselves. But never actually went as far as to void the guarantees."
Brown never played a game for Oakland but was the center of the Raiders' offseason story.
AB runs around screaming 'I'm free' after being released
Antonio Brown runs around his backyard screaming after he was released by the Raiders.
He spent time away from the team as he attempted to resolve issues with his helmet and his feet, was fined for missing time, got into a verbal altercation with general manager Mike Mayock over those fines and was fined for the altercation.
Additionally, Brown on Friday posted a video on YouTube of a private phone call he had with Raiders coach Jon Gruden.
In the video, which lasted 1 minute, 57 seconds, Brown is heard taking a call from Gruden, who asks the receiver: "What the hell is going on, man?"
Brown answers, "Just a villain all over the news, man."
After Brown's release, Gruden was asked about the receiver.
"I tell you, he's a good guy," the coach said. "He's misunderstood by a lot of people. He's a good guy. He's a great player, and I hope he gets what he's looking for."
The acquisition of Brown moved the Patriots past the Kansas City Chiefs and into the role of Super Bowl favorites. The Patriots went from 6-1 to 4-1 to win the Super Bowl, per Caesars Sportsbook. The Chiefs are 6-1. New England's updated win total moved from 11 to 11.5, per Caesars.
The Patriots have done well taking on players whose careers eventually were reborn in New England. Recent examples under coach Bill Belichick were running back Corey Dillon (rushed for 1,635 yards and won Super Bowl in 2004 season after being acquired via trade), receiver Wes Welker (caught NFL-high 112 passes in 2007 season after being acquired via trade) and receiver Randy Moss (caught 23 touchdowns in 2007 season after being acquired via trade).
Brown will try to follow suit.
Dating to 2010, his rookie season, he leads the league in receptions (837), receiving yards (11,207) and first downs (546) and is second to the now-retired Patriot Rob Gronkowski (79) in receiving touchdowns (74) during that span.
Moss (three times) and Gronkowski (five) are the only players to record double-digit touchdown receptions for the Patriots since 2001. Brown recorded double-digit TDs in four of his last five seasons with the Steelers, including his league-leading 15 TD receptions last season.
ESPN's Mike Reiss and David Purdum contributed to this report.