Talk about getting thrown into the fire.
NFL.com first reported the deal, which is pending a physical.
At least Law has familiarity on his side. He played from 1995 to 2004 in New England before spending the 2005 season with the Jets. Law worked with current Jets coach Eric Mangini in New England. Mangini was the defensive backs coach from 2000 to '04 before taking over the Jets in 2006.
Law was with the Chiefs the past two seasons but became a free agent at the end of the year.
"This is going to be different playing Thursday night against the Patriots, matching up against my former team and the players I'm used to practicing against," Law said from Boston, according to NFL.com.
"I know they're going to throw at me, but I welcome the challenge -- bring it. I got the tricks for you."
Law is a five-time Pro Bowler who has 52 career interceptions. NFL.com reported that the Patriots had also been in contact with Law, trying to bring him back.
"I just feel better about this and the direction this team is going and how they welcomed me," Law said, according to the Web site. "I wanted to be somewhere I wanted."
Law told NFL.com that the Jets plan to use him at both cornerback and safety. Cornerback Darrelle Revis, who has started every game in his first two NFL seasons, looked up to Law while growing up in the same hometown of Aliquippa, Pa., and even wears Law's No. 24.
"That's my little boy," Law told NFL.com. "I've watched him grow up and to be able to help him now, it'll be a good deal."
Law, no longer the shutdown corner he once was, also might play opposite Revis at times. Rookie Dwight Lowery has started all nine games, but has looked shaky recently.
The Jets will have to make a corresponding roster move to make room for Law. Along with Revis, Lowery and now Law, New York also has cornerbacks Justin Miller, Hank Poteat, David Barrett and Ahmad Carroll, along with two kickers in Jay Feely and Mike Nugent.
Law, a first-round pick out of Michigan by the Patriots in 1995, helped New England to three Super Bowl titles. He signed with the Jets in 2005 after being released by the Patriots, and had a career-high 10 interceptions and was voted to the Pro Bowl.
He was released by the Jets after that season and followed coach Herm Edwards to Kansas City, where he played two years before being cut in the offseason.
Information from The Associated Press was used in this report.