The parties were scheduled for an arbitration hearing on July 29.
“I think this is a good deal for both sides,” Devils general manager Ray Shero told Northjersey.com. “This is a young defenseman at 22 years old who is signed for a six-year term. Adam showed a commitment that he really wanted to be here, and we got him three years past the age of unrestricted free agency.
“I think he's only scratched the surface of the kind of player he's going to be. There's a reason he was drafted when he was.”
Larsson was the fourth pick in the 2011 NHL draft, and played his first game for the Devils during the 2011-12 season.
In 64 games last season, Larsson led Devils defensemen with a career-high 21 assists and 24 points.