Financial terms weren't disclosed.
Versus, the television network on which Seau has a show, announced the deal Tuesday. The Patriots haven't officially announced the move, which had been expected, although the team said the 12-time Pro Bowler had a physical and a workout last week. The Patriots also haven't made a roster move to clear space for Seau.
"I hope at some point he will be (with the team)," Patriots owner Robert Kraft said at the NFL Fall League Meeting in Boston. "He's a unique individual. I'd love to have him part of our team for as long as he wants to."
Seau, 40, should have a better chance of standing up to running backs than he did to a rodeo bull, which knocked him down on one of the episodes of "Sports Jobs with Junior Seau." He came out of retirement last year to play the final four games with the Patriots after playing 27 games with them in 2006 and 2007.
One week before New England began its 2009 season, Seau said he'd only consider playing for the Patriots and would be willing to do six games. The team has 11 games left.
"I'm very fortunate and honored to be involved with two class organizations -- the New England Patriots and Versus," Seau said in a statement released by Versus. "I want to thank the management of both for making my return to the NFL with the New England Patriots a reality."
The 10-episode series begins on Dec. 2. Among Seau's activities are riding a Zamboni at a hockey game between the Boston Bruins and Washington Capitals, working as a ballboy along the left-field line for the Los Angeles Dodgers and carrying a golf bag as an LPGA caddy.
Seau's return to the Patriots won't affect his role as host of the series, Versus president Jamie Davis said.
On the Patriots, Seau can provide veteran leadership to a defense that lost safety Rodney Harrison and linebacker Tedy Bruschi to retirement and linebacker Mike Vrabel and Richard Seymour in trades. Seau also provides depth at inside linebacker, a position where the only backup, Eric Alexander, has primarily played on special teams.
"Did I miss it? Did we announce anything?" Belichick questioned Patriots assistant director of media relations Aaron Salkin when asked to comment on the announced signing.
When told the team hadn't announced it, Belichick said, "I didn't think so. ... We don't have anything to say about it."
Director of player personnel Nick Caserio said on his regular conference call immediately following Belichick's that the Patriots gave Seau a physical and worked him out last week.
"He looked like he's kept himself in shape," Caserio said. "We wanted to make sure, more than anything, from a physical standpoint with the medical information, that he was healthy."
"I'm not retiring. I am graduating. Today is my graduation day," he said then. "Retirement means that you'll just go ahead and live on your laurels and surf all day in Oceanside (Calif.). It ain't going to happen."
Four days later, Seau signed with the Patriots.
Seau started 10 of the 11 games he played in 2006 before breaking his arm and four of his 16 in 2007. He came out of retirement for a second time for the final four games last season when the Patriots were hit hard by injuries at linebacker.
The Associated Press contributed to this report.